1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761 1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783 1784 1785 1786 1787 1788 1789 1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810 1811 1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871 1872 1873 1874 1875 1876 1877 1878 1879 1880 1881 1882 1883 1884 1885
//! A priority queue implemented with a binary heap.
//!
//! Insertion and popping the largest element have *O*(log(*n*)) time complexity.
//! Checking the largest element is *O*(1). Converting a vector to a binary heap
//! can be done in-place, and has *O*(*n*) complexity. A binary heap can also be
//! converted to a sorted vector in-place, allowing it to be used for an *O*(*n* * log(*n*))
//! in-place heapsort.
//!
//! # Examples
//!
//! This is a larger example that implements [Dijkstra's algorithm][dijkstra]
//! to solve the [shortest path problem][sssp] on a [directed graph][dir_graph].
//! It shows how to use [`BinaryHeap`] with custom types.
//!
//! [dijkstra]: https://en.wikipedia.org/wiki/Dijkstra%27s_algorithm
//! [sssp]: https://en.wikipedia.org/wiki/Shortest_path_problem
//! [dir_graph]: https://en.wikipedia.org/wiki/Directed_graph
//!
//! ```
//! use std::cmp::Ordering;
//! use std::collections::BinaryHeap;
//!
//! #[derive(Copy, Clone, Eq, PartialEq)]
//! struct State {
//! cost: usize,
//! position: usize,
//! }
//!
//! // The priority queue depends on `Ord`.
//! // Explicitly implement the trait so the queue becomes a min-heap
//! // instead of a max-heap.
//! impl Ord for State {
//! fn cmp(&self, other: &Self) -> Ordering {
//! // Notice that we flip the ordering on costs.
//! // In case of a tie we compare positions - this step is necessary
//! // to make implementations of `PartialEq` and `Ord` consistent.
//! other.cost.cmp(&self.cost)
//! .then_with(|| self.position.cmp(&other.position))
//! }
//! }
//!
//! // `PartialOrd` needs to be implemented as well.
//! impl PartialOrd for State {
//! fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
//! Some(self.cmp(other))
//! }
//! }
//!
//! // Each node is represented as a `usize`, for a shorter implementation.
//! struct Edge {
//! node: usize,
//! cost: usize,
//! }
//!
//! // Dijkstra's shortest path algorithm.
//!
//! // Start at `start` and use `dist` to track the current shortest distance
//! // to each node. This implementation isn't memory-efficient as it may leave duplicate
//! // nodes in the queue. It also uses `usize::MAX` as a sentinel value,
//! // for a simpler implementation.
//! fn shortest_path(adj_list: &Vec<Vec<Edge>>, start: usize, goal: usize) -> Option<usize> {
//! // dist[node] = current shortest distance from `start` to `node`
//! let mut dist: Vec<_> = (0..adj_list.len()).map(|_| usize::MAX).collect();
//!
//! let mut heap = BinaryHeap::new();
//!
//! // We're at `start`, with a zero cost
//! dist[start] = 0;
//! heap.push(State { cost: 0, position: start });
//!
//! // Examine the frontier with lower cost nodes first (min-heap)
//! while let Some(State { cost, position }) = heap.pop() {
//! // Alternatively we could have continued to find all shortest paths
//! if position == goal { return Some(cost); }
//!
//! // Important as we may have already found a better way
//! if cost > dist[position] { continue; }
//!
//! // For each node we can reach, see if we can find a way with
//! // a lower cost going through this node
//! for edge in &adj_list[position] {
//! let next = State { cost: cost + edge.cost, position: edge.node };
//!
//! // If so, add it to the frontier and continue
//! if next.cost < dist[next.position] {
//! heap.push(next);
//! // Relaxation, we have now found a better way
//! dist[next.position] = next.cost;
//! }
//! }
//! }
//!
//! // Goal not reachable
//! None
//! }
//!
//! fn main() {
//! // This is the directed graph we're going to use.
//! // The node numbers correspond to the different states,
//! // and the edge weights symbolize the cost of moving
//! // from one node to another.
//! // Note that the edges are one-way.
//! //
//! // 7
//! // +-----------------+
//! // | |
//! // v 1 2 | 2
//! // 0 -----> 1 -----> 3 ---> 4
//! // | ^ ^ ^
//! // | | 1 | |
//! // | | | 3 | 1
//! // +------> 2 -------+ |
//! // 10 | |
//! // +---------------+
//! //
//! // The graph is represented as an adjacency list where each index,
//! // corresponding to a node value, has a list of outgoing edges.
//! // Chosen for its efficiency.
//! let graph = vec![
//! // Node 0
//! vec![Edge { node: 2, cost: 10 },
//! Edge { node: 1, cost: 1 }],
//! // Node 1
//! vec![Edge { node: 3, cost: 2 }],
//! // Node 2
//! vec![Edge { node: 1, cost: 1 },
//! Edge { node: 3, cost: 3 },
//! Edge { node: 4, cost: 1 }],
//! // Node 3
//! vec![Edge { node: 0, cost: 7 },
//! Edge { node: 4, cost: 2 }],
//! // Node 4
//! vec![]];
//!
//! assert_eq!(shortest_path(&graph, 0, 1), Some(1));
//! assert_eq!(shortest_path(&graph, 0, 3), Some(3));
//! assert_eq!(shortest_path(&graph, 3, 0), Some(7));
//! assert_eq!(shortest_path(&graph, 0, 4), Some(5));
//! assert_eq!(shortest_path(&graph, 4, 0), None);
//! }
//! ```
#![allow(missing_docs)]
#![stable(feature = "rust1", since = "1.0.0")]
use core::alloc::Allocator;
use core::fmt;
use core::iter::{FusedIterator, InPlaceIterable, SourceIter, TrustedFused, TrustedLen};
use core::mem::{self, swap, ManuallyDrop};
use core::num::NonZero;
use core::ops::{Deref, DerefMut};
use core::ptr;
use crate::alloc::Global;
use crate::collections::TryReserveError;
use crate::slice;
use crate::vec::{self, AsVecIntoIter, Vec};
#[cfg(test)]
mod tests;
/// A priority queue implemented with a binary heap.
///
/// This will be a max-heap.
///
/// It is a logic error for an item to be modified in such a way that the
/// item's ordering relative to any other item, as determined by the [`Ord`]
/// trait, changes while it is in the heap. This is normally only possible
/// through interior mutability, global state, I/O, or unsafe code. The
/// behavior resulting from such a logic error is not specified, but will
/// be encapsulated to the `BinaryHeap` that observed the logic error and not
/// result in undefined behavior. This could include panics, incorrect results,
/// aborts, memory leaks, and non-termination.
///
/// As long as no elements change their relative order while being in the heap
/// as described above, the API of `BinaryHeap` guarantees that the heap
/// invariant remains intact i.e. its methods all behave as documented. For
/// example if a method is documented as iterating in sorted order, that's
/// guaranteed to work as long as elements in the heap have not changed order,
/// even in the presence of closures getting unwinded out of, iterators getting
/// leaked, and similar foolishness.
///
/// # Examples
///
/// ```
/// use std::collections::BinaryHeap;
///
/// // Type inference lets us omit an explicit type signature (which
/// // would be `BinaryHeap<i32>` in this example).
/// let mut heap = BinaryHeap::new();
///
/// // We can use peek to look at the next item in the heap. In this case,
/// // there's no items in there yet so we get None.
/// assert_eq!(heap.peek(), None);
///
/// // Let's add some scores...
/// heap.push(1);
/// heap.push(5);
/// heap.push(2);
///
/// // Now peek shows the most important item in the heap.
/// assert_eq!(heap.peek(), Some(&5));
///
/// // We can check the length of a heap.
/// assert_eq!(heap.len(), 3);
///
/// // We can iterate over the items in the heap, although they are returned in
/// // a random order.
/// for x in &heap {
/// println!("{x}");
/// }
///
/// // If we instead pop these scores, they should come back in order.
/// assert_eq!(heap.pop(), Some(5));
/// assert_eq!(heap.pop(), Some(2));
/// assert_eq!(heap.pop(), Some(1));
/// assert_eq!(heap.pop(), None);
///
/// // We can clear the heap of any remaining items.
/// heap.clear();
///
/// // The heap should now be empty.
/// assert!(heap.is_empty())
/// ```
///
/// A `BinaryHeap` with a known list of items can be initialized from an array:
///
/// ```
/// use std::collections::BinaryHeap;
///
/// let heap = BinaryHeap::from([1, 5, 2]);
/// ```
///
/// ## Min-heap
///
/// Either [`core::cmp::Reverse`] or a custom [`Ord`] implementation can be used to
/// make `BinaryHeap` a min-heap. This makes `heap.pop()` return the smallest
/// value instead of the greatest one.
///
/// ```
/// use std::collections::BinaryHeap;
/// use std::cmp::Reverse;
///
/// let mut heap = BinaryHeap::new();
///
/// // Wrap values in `Reverse`
/// heap.push(Reverse(1));
/// heap.push(Reverse(5));
/// heap.push(Reverse(2));
///
/// // If we pop these scores now, they should come back in the reverse order.
/// assert_eq!(heap.pop(), Some(Reverse(1)));
/// assert_eq!(heap.pop(), Some(Reverse(2)));
/// assert_eq!(heap.pop(), Some(Reverse(5)));
/// assert_eq!(heap.pop(), None);
/// ```
///
/// # Time complexity
///
/// | [push] | [pop] | [peek]/[peek\_mut] |
/// |---------|---------------|--------------------|
/// | *O*(1)~ | *O*(log(*n*)) | *O*(1) |
///
/// The value for `push` is an expected cost; the method documentation gives a
/// more detailed analysis.
///
/// [`core::cmp::Reverse`]: core::cmp::Reverse
/// [`Cell`]: core::cell::Cell
/// [`RefCell`]: core::cell::RefCell
/// [push]: BinaryHeap::push
/// [pop]: BinaryHeap::pop
/// [peek]: BinaryHeap::peek
/// [peek\_mut]: BinaryHeap::peek_mut
#[stable(feature = "rust1", since = "1.0.0")]
#[cfg_attr(not(test), rustc_diagnostic_item = "BinaryHeap")]
pub struct BinaryHeap<
T,
#[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
> {
data: Vec<T, A>,
}
/// Structure wrapping a mutable reference to the greatest item on a
/// `BinaryHeap`.
///
/// This `struct` is created by the [`peek_mut`] method on [`BinaryHeap`]. See
/// its documentation for more.
///
/// [`peek_mut`]: BinaryHeap::peek_mut
#[stable(feature = "binary_heap_peek_mut", since = "1.12.0")]
pub struct PeekMut<
'a,
T: 'a + Ord,
#[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
> {
heap: &'a mut BinaryHeap<T, A>,
// If a set_len + sift_down are required, this is Some. If a &mut T has not
// yet been exposed to peek_mut()'s caller, it's None.
original_len: Option<NonZero<usize>>,
}
#[stable(feature = "collection_debug", since = "1.17.0")]
impl<T: Ord + fmt::Debug, A: Allocator> fmt::Debug for PeekMut<'_, T, A> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_tuple("PeekMut").field(&self.heap.data[0]).finish()
}
}
#[stable(feature = "binary_heap_peek_mut", since = "1.12.0")]
impl<T: Ord, A: Allocator> Drop for PeekMut<'_, T, A> {
fn drop(&mut self) {
if let Some(original_len) = self.original_len {
// SAFETY: That's how many elements were in the Vec at the time of
// the PeekMut::deref_mut call, and therefore also at the time of
// the BinaryHeap::peek_mut call. Since the PeekMut did not end up
// getting leaked, we are now undoing the leak amplification that
// the DerefMut prepared for.
unsafe { self.heap.data.set_len(original_len.get()) };
// SAFETY: PeekMut is only instantiated for non-empty heaps.
unsafe { self.heap.sift_down(0) };
}
}
}
#[stable(feature = "binary_heap_peek_mut", since = "1.12.0")]
impl<T: Ord, A: Allocator> Deref for PeekMut<'_, T, A> {
type Target = T;
fn deref(&self) -> &T {
debug_assert!(!self.heap.is_empty());
// SAFE: PeekMut is only instantiated for non-empty heaps
unsafe { self.heap.data.get_unchecked(0) }
}
}
#[stable(feature = "binary_heap_peek_mut", since = "1.12.0")]
impl<T: Ord, A: Allocator> DerefMut for PeekMut<'_, T, A> {
fn deref_mut(&mut self) -> &mut T {
debug_assert!(!self.heap.is_empty());
let len = self.heap.len();
if len > 1 {
// Here we preemptively leak all the rest of the underlying vector
// after the currently max element. If the caller mutates the &mut T
// we're about to give them, and then leaks the PeekMut, all these
// elements will remain leaked. If they don't leak the PeekMut, then
// either Drop or PeekMut::pop will un-leak the vector elements.
//
// This is technique is described throughout several other places in
// the standard library as "leak amplification".
unsafe {
// SAFETY: len > 1 so len != 0.
self.original_len = Some(NonZero::new_unchecked(len));
// SAFETY: len > 1 so all this does for now is leak elements,
// which is safe.
self.heap.data.set_len(1);
}
}
// SAFE: PeekMut is only instantiated for non-empty heaps
unsafe { self.heap.data.get_unchecked_mut(0) }
}
}
impl<'a, T: Ord, A: Allocator> PeekMut<'a, T, A> {
/// Removes the peeked value from the heap and returns it.
#[stable(feature = "binary_heap_peek_mut_pop", since = "1.18.0")]
pub fn pop(mut this: PeekMut<'a, T, A>) -> T {
if let Some(original_len) = this.original_len.take() {
// SAFETY: This is how many elements were in the Vec at the time of
// the BinaryHeap::peek_mut call.
unsafe { this.heap.data.set_len(original_len.get()) };
// Unlike in Drop, here we don't also need to do a sift_down even if
// the caller could've mutated the element. It is removed from the
// heap on the next line and pop() is not sensitive to its value.
}
this.heap.pop().unwrap()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Clone, A: Allocator + Clone> Clone for BinaryHeap<T, A> {
fn clone(&self) -> Self {
BinaryHeap { data: self.data.clone() }
}
/// Overwrites the contents of `self` with a clone of the contents of `source`.
///
/// This method is preferred over simply assigning `source.clone()` to `self`,
/// as it avoids reallocation if possible.
///
/// See [`Vec::clone_from()`] for more details.
fn clone_from(&mut self, source: &Self) {
self.data.clone_from(&source.data);
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Ord> Default for BinaryHeap<T> {
/// Creates an empty `BinaryHeap<T>`.
#[inline]
fn default() -> BinaryHeap<T> {
BinaryHeap::new()
}
}
#[stable(feature = "binaryheap_debug", since = "1.4.0")]
impl<T: fmt::Debug, A: Allocator> fmt::Debug for BinaryHeap<T, A> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_list().entries(self.iter()).finish()
}
}
struct RebuildOnDrop<
'a,
T: Ord,
#[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
> {
heap: &'a mut BinaryHeap<T, A>,
rebuild_from: usize,
}
impl<T: Ord, A: Allocator> Drop for RebuildOnDrop<'_, T, A> {
fn drop(&mut self) {
self.heap.rebuild_tail(self.rebuild_from);
}
}
impl<T: Ord> BinaryHeap<T> {
/// Creates an empty `BinaryHeap` as a max-heap.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// let mut heap = BinaryHeap::new();
/// heap.push(4);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_binary_heap_constructor", since = "1.80.0")]
#[must_use]
pub const fn new() -> BinaryHeap<T> {
BinaryHeap { data: vec![] }
}
/// Creates an empty `BinaryHeap` with at least the specified capacity.
///
/// The binary heap will be able to hold at least `capacity` elements without
/// reallocating. This method is allowed to allocate for more elements than
/// `capacity`. If `capacity` is 0, the binary heap will not allocate.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// let mut heap = BinaryHeap::with_capacity(10);
/// heap.push(4);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[must_use]
pub fn with_capacity(capacity: usize) -> BinaryHeap<T> {
BinaryHeap { data: Vec::with_capacity(capacity) }
}
}
impl<T: Ord, A: Allocator> BinaryHeap<T, A> {
/// Creates an empty `BinaryHeap` as a max-heap, using `A` as allocator.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(allocator_api)]
///
/// use std::alloc::System;
/// use std::collections::BinaryHeap;
/// let mut heap = BinaryHeap::new_in(System);
/// heap.push(4);
/// ```
#[unstable(feature = "allocator_api", issue = "32838")]
#[rustc_const_unstable(feature = "const_binary_heap_new_in", issue = "112353")]
#[must_use]
pub const fn new_in(alloc: A) -> BinaryHeap<T, A> {
BinaryHeap { data: Vec::new_in(alloc) }
}
/// Creates an empty `BinaryHeap` with at least the specified capacity, using `A` as allocator.
///
/// The binary heap will be able to hold at least `capacity` elements without
/// reallocating. This method is allowed to allocate for more elements than
/// `capacity`. If `capacity` is 0, the binary heap will not allocate.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(allocator_api)]
///
/// use std::alloc::System;
/// use std::collections::BinaryHeap;
/// let mut heap = BinaryHeap::with_capacity_in(10, System);
/// heap.push(4);
/// ```
#[unstable(feature = "allocator_api", issue = "32838")]
#[must_use]
pub fn with_capacity_in(capacity: usize, alloc: A) -> BinaryHeap<T, A> {
BinaryHeap { data: Vec::with_capacity_in(capacity, alloc) }
}
/// Returns a mutable reference to the greatest item in the binary heap, or
/// `None` if it is empty.
///
/// Note: If the `PeekMut` value is leaked, some heap elements might get
/// leaked along with it, but the remaining elements will remain a valid
/// heap.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// let mut heap = BinaryHeap::new();
/// assert!(heap.peek_mut().is_none());
///
/// heap.push(1);
/// heap.push(5);
/// heap.push(2);
/// {
/// let mut val = heap.peek_mut().unwrap();
/// *val = 0;
/// }
/// assert_eq!(heap.peek(), Some(&2));
/// ```
///
/// # Time complexity
///
/// If the item is modified then the worst case time complexity is *O*(log(*n*)),
/// otherwise it's *O*(1).
#[stable(feature = "binary_heap_peek_mut", since = "1.12.0")]
pub fn peek_mut(&mut self) -> Option<PeekMut<'_, T, A>> {
if self.is_empty() { None } else { Some(PeekMut { heap: self, original_len: None }) }
}
/// Removes the greatest item from the binary heap and returns it, or `None` if it
/// is empty.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// let mut heap = BinaryHeap::from([1, 3]);
///
/// assert_eq!(heap.pop(), Some(3));
/// assert_eq!(heap.pop(), Some(1));
/// assert_eq!(heap.pop(), None);
/// ```
///
/// # Time complexity
///
/// The worst case cost of `pop` on a heap containing *n* elements is *O*(log(*n*)).
#[stable(feature = "rust1", since = "1.0.0")]
pub fn pop(&mut self) -> Option<T> {
self.data.pop().map(|mut item| {
if !self.is_empty() {
swap(&mut item, &mut self.data[0]);
// SAFETY: !self.is_empty() means that self.len() > 0
unsafe { self.sift_down_to_bottom(0) };
}
item
})
}
/// Pushes an item onto the binary heap.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// let mut heap = BinaryHeap::new();
/// heap.push(3);
/// heap.push(5);
/// heap.push(1);
///
/// assert_eq!(heap.len(), 3);
/// assert_eq!(heap.peek(), Some(&5));
/// ```
///
/// # Time complexity
///
/// The expected cost of `push`, averaged over every possible ordering of
/// the elements being pushed, and over a sufficiently large number of
/// pushes, is *O*(1). This is the most meaningful cost metric when pushing
/// elements that are *not* already in any sorted pattern.
///
/// The time complexity degrades if elements are pushed in predominantly
/// ascending order. In the worst case, elements are pushed in ascending
/// sorted order and the amortized cost per push is *O*(log(*n*)) against a heap
/// containing *n* elements.
///
/// The worst case cost of a *single* call to `push` is *O*(*n*). The worst case
/// occurs when capacity is exhausted and needs a resize. The resize cost
/// has been amortized in the previous figures.
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_confusables("append", "put")]
pub fn push(&mut self, item: T) {
let old_len = self.len();
self.data.push(item);
// SAFETY: Since we pushed a new item it means that
// old_len = self.len() - 1 < self.len()
unsafe { self.sift_up(0, old_len) };
}
/// Consumes the `BinaryHeap` and returns a vector in sorted
/// (ascending) order.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
///
/// let mut heap = BinaryHeap::from([1, 2, 4, 5, 7]);
/// heap.push(6);
/// heap.push(3);
///
/// let vec = heap.into_sorted_vec();
/// assert_eq!(vec, [1, 2, 3, 4, 5, 6, 7]);
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "binary_heap_extras_15", since = "1.5.0")]
pub fn into_sorted_vec(mut self) -> Vec<T, A> {
let mut end = self.len();
while end > 1 {
end -= 1;
// SAFETY: `end` goes from `self.len() - 1` to 1 (both included),
// so it's always a valid index to access.
// It is safe to access index 0 (i.e. `ptr`), because
// 1 <= end < self.len(), which means self.len() >= 2.
unsafe {
let ptr = self.data.as_mut_ptr();
ptr::swap(ptr, ptr.add(end));
}
// SAFETY: `end` goes from `self.len() - 1` to 1 (both included) so:
// 0 < 1 <= end <= self.len() - 1 < self.len()
// Which means 0 < end and end < self.len().
unsafe { self.sift_down_range(0, end) };
}
self.into_vec()
}
// The implementations of sift_up and sift_down use unsafe blocks in
// order to move an element out of the vector (leaving behind a
// hole), shift along the others and move the removed element back into the
// vector at the final location of the hole.
// The `Hole` type is used to represent this, and make sure
// the hole is filled back at the end of its scope, even on panic.
// Using a hole reduces the constant factor compared to using swaps,
// which involves twice as many moves.
/// # Safety
///
/// The caller must guarantee that `pos < self.len()`.
unsafe fn sift_up(&mut self, start: usize, pos: usize) -> usize {
// Take out the value at `pos` and create a hole.
// SAFETY: The caller guarantees that pos < self.len()
let mut hole = unsafe { Hole::new(&mut self.data, pos) };
while hole.pos() > start {
let parent = (hole.pos() - 1) / 2;
// SAFETY: hole.pos() > start >= 0, which means hole.pos() > 0
// and so hole.pos() - 1 can't underflow.
// This guarantees that parent < hole.pos() so
// it's a valid index and also != hole.pos().
if hole.element() <= unsafe { hole.get(parent) } {
break;
}
// SAFETY: Same as above
unsafe { hole.move_to(parent) };
}
hole.pos()
}
/// Take an element at `pos` and move it down the heap,
/// while its children are larger.
///
/// # Safety
///
/// The caller must guarantee that `pos < end <= self.len()`.
unsafe fn sift_down_range(&mut self, pos: usize, end: usize) {
// SAFETY: The caller guarantees that pos < end <= self.len().
let mut hole = unsafe { Hole::new(&mut self.data, pos) };
let mut child = 2 * hole.pos() + 1;
// Loop invariant: child == 2 * hole.pos() + 1.
while child <= end.saturating_sub(2) {
// compare with the greater of the two children
// SAFETY: child < end - 1 < self.len() and
// child + 1 < end <= self.len(), so they're valid indexes.
// child == 2 * hole.pos() + 1 != hole.pos() and
// child + 1 == 2 * hole.pos() + 2 != hole.pos().
// FIXME: 2 * hole.pos() + 1 or 2 * hole.pos() + 2 could overflow
// if T is a ZST
child += unsafe { hole.get(child) <= hole.get(child + 1) } as usize;
// if we are already in order, stop.
// SAFETY: child is now either the old child or the old child+1
// We already proven that both are < self.len() and != hole.pos()
if hole.element() >= unsafe { hole.get(child) } {
return;
}
// SAFETY: same as above.
unsafe { hole.move_to(child) };
child = 2 * hole.pos() + 1;
}
// SAFETY: && short circuit, which means that in the
// second condition it's already true that child == end - 1 < self.len().
if child == end - 1 && hole.element() < unsafe { hole.get(child) } {
// SAFETY: child is already proven to be a valid index and
// child == 2 * hole.pos() + 1 != hole.pos().
unsafe { hole.move_to(child) };
}
}
/// # Safety
///
/// The caller must guarantee that `pos < self.len()`.
unsafe fn sift_down(&mut self, pos: usize) {
let len = self.len();
// SAFETY: pos < len is guaranteed by the caller and
// obviously len = self.len() <= self.len().
unsafe { self.sift_down_range(pos, len) };
}
/// Take an element at `pos` and move it all the way down the heap,
/// then sift it up to its position.
///
/// Note: This is faster when the element is known to be large / should
/// be closer to the bottom.
///
/// # Safety
///
/// The caller must guarantee that `pos < self.len()`.
unsafe fn sift_down_to_bottom(&mut self, mut pos: usize) {
let end = self.len();
let start = pos;
// SAFETY: The caller guarantees that pos < self.len().
let mut hole = unsafe { Hole::new(&mut self.data, pos) };
let mut child = 2 * hole.pos() + 1;
// Loop invariant: child == 2 * hole.pos() + 1.
while child <= end.saturating_sub(2) {
// SAFETY: child < end - 1 < self.len() and
// child + 1 < end <= self.len(), so they're valid indexes.
// child == 2 * hole.pos() + 1 != hole.pos() and
// child + 1 == 2 * hole.pos() + 2 != hole.pos().
// FIXME: 2 * hole.pos() + 1 or 2 * hole.pos() + 2 could overflow
// if T is a ZST
child += unsafe { hole.get(child) <= hole.get(child + 1) } as usize;
// SAFETY: Same as above
unsafe { hole.move_to(child) };
child = 2 * hole.pos() + 1;
}
if child == end - 1 {
// SAFETY: child == end - 1 < self.len(), so it's a valid index
// and child == 2 * hole.pos() + 1 != hole.pos().
unsafe { hole.move_to(child) };
}
pos = hole.pos();
drop(hole);
// SAFETY: pos is the position in the hole and was already proven
// to be a valid index.
unsafe { self.sift_up(start, pos) };
}
/// Rebuild assuming data[0..start] is still a proper heap.
fn rebuild_tail(&mut self, start: usize) {
if start == self.len() {
return;
}
let tail_len = self.len() - start;
#[inline(always)]
fn log2_fast(x: usize) -> usize {
(usize::BITS - x.leading_zeros() - 1) as usize
}
// `rebuild` takes O(self.len()) operations
// and about 2 * self.len() comparisons in the worst case
// while repeating `sift_up` takes O(tail_len * log(start)) operations
// and about 1 * tail_len * log_2(start) comparisons in the worst case,
// assuming start >= tail_len. For larger heaps, the crossover point
// no longer follows this reasoning and was determined empirically.
let better_to_rebuild = if start < tail_len {
true
} else if self.len() <= 2048 {
2 * self.len() < tail_len * log2_fast(start)
} else {
2 * self.len() < tail_len * 11
};
if better_to_rebuild {
self.rebuild();
} else {
for i in start..self.len() {
// SAFETY: The index `i` is always less than self.len().
unsafe { self.sift_up(0, i) };
}
}
}
fn rebuild(&mut self) {
let mut n = self.len() / 2;
while n > 0 {
n -= 1;
// SAFETY: n starts from self.len() / 2 and goes down to 0.
// The only case when !(n < self.len()) is if
// self.len() == 0, but it's ruled out by the loop condition.
unsafe { self.sift_down(n) };
}
}
/// Moves all the elements of `other` into `self`, leaving `other` empty.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
///
/// let mut a = BinaryHeap::from([-10, 1, 2, 3, 3]);
/// let mut b = BinaryHeap::from([-20, 5, 43]);
///
/// a.append(&mut b);
///
/// assert_eq!(a.into_sorted_vec(), [-20, -10, 1, 2, 3, 3, 5, 43]);
/// assert!(b.is_empty());
/// ```
#[stable(feature = "binary_heap_append", since = "1.11.0")]
pub fn append(&mut self, other: &mut Self) {
if self.len() < other.len() {
swap(self, other);
}
let start = self.data.len();
self.data.append(&mut other.data);
self.rebuild_tail(start);
}
/// Clears the binary heap, returning an iterator over the removed elements
/// in heap order. If the iterator is dropped before being fully consumed,
/// it drops the remaining elements in heap order.
///
/// The returned iterator keeps a mutable borrow on the heap to optimize
/// its implementation.
///
/// Note:
/// * `.drain_sorted()` is *O*(*n* \* log(*n*)); much slower than `.drain()`.
/// You should use the latter for most cases.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(binary_heap_drain_sorted)]
/// use std::collections::BinaryHeap;
///
/// let mut heap = BinaryHeap::from([1, 2, 3, 4, 5]);
/// assert_eq!(heap.len(), 5);
///
/// drop(heap.drain_sorted()); // removes all elements in heap order
/// assert_eq!(heap.len(), 0);
/// ```
#[inline]
#[unstable(feature = "binary_heap_drain_sorted", issue = "59278")]
pub fn drain_sorted(&mut self) -> DrainSorted<'_, T, A> {
DrainSorted { inner: self }
}
/// Retains only the elements specified by the predicate.
///
/// In other words, remove all elements `e` for which `f(&e)` returns
/// `false`. The elements are visited in unsorted (and unspecified) order.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
///
/// let mut heap = BinaryHeap::from([-10, -5, 1, 2, 4, 13]);
///
/// heap.retain(|x| x % 2 == 0); // only keep even numbers
///
/// assert_eq!(heap.into_sorted_vec(), [-10, 2, 4])
/// ```
#[stable(feature = "binary_heap_retain", since = "1.70.0")]
pub fn retain<F>(&mut self, mut f: F)
where
F: FnMut(&T) -> bool,
{
// rebuild_start will be updated to the first touched element below, and the rebuild will
// only be done for the tail.
let mut guard = RebuildOnDrop { rebuild_from: self.len(), heap: self };
let mut i = 0;
guard.heap.data.retain(|e| {
let keep = f(e);
if !keep && i < guard.rebuild_from {
guard.rebuild_from = i;
}
i += 1;
keep
});
}
}
impl<T, A: Allocator> BinaryHeap<T, A> {
/// Returns an iterator visiting all values in the underlying vector, in
/// arbitrary order.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// let heap = BinaryHeap::from([1, 2, 3, 4]);
///
/// // Print 1, 2, 3, 4 in arbitrary order
/// for x in heap.iter() {
/// println!("{x}");
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn iter(&self) -> Iter<'_, T> {
Iter { iter: self.data.iter() }
}
/// Returns an iterator which retrieves elements in heap order.
/// This method consumes the original heap.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(binary_heap_into_iter_sorted)]
/// use std::collections::BinaryHeap;
/// let heap = BinaryHeap::from([1, 2, 3, 4, 5]);
///
/// assert_eq!(heap.into_iter_sorted().take(2).collect::<Vec<_>>(), [5, 4]);
/// ```
#[unstable(feature = "binary_heap_into_iter_sorted", issue = "59278")]
pub fn into_iter_sorted(self) -> IntoIterSorted<T, A> {
IntoIterSorted { inner: self }
}
/// Returns the greatest item in the binary heap, or `None` if it is empty.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// let mut heap = BinaryHeap::new();
/// assert_eq!(heap.peek(), None);
///
/// heap.push(1);
/// heap.push(5);
/// heap.push(2);
/// assert_eq!(heap.peek(), Some(&5));
///
/// ```
///
/// # Time complexity
///
/// Cost is *O*(1) in the worst case.
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn peek(&self) -> Option<&T> {
self.data.get(0)
}
/// Returns the number of elements the binary heap can hold without reallocating.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// let mut heap = BinaryHeap::with_capacity(100);
/// assert!(heap.capacity() >= 100);
/// heap.push(4);
/// ```
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn capacity(&self) -> usize {
self.data.capacity()
}
/// Reserves the minimum capacity for at least `additional` elements more than
/// the current length. Unlike [`reserve`], this will not
/// deliberately over-allocate to speculatively avoid frequent allocations.
/// After calling `reserve_exact`, capacity will be greater than or equal to
/// `self.len() + additional`. Does nothing if the capacity is already
/// sufficient.
///
/// [`reserve`]: BinaryHeap::reserve
///
/// # Panics
///
/// Panics if the new capacity overflows [`usize`].
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// let mut heap = BinaryHeap::new();
/// heap.reserve_exact(100);
/// assert!(heap.capacity() >= 100);
/// heap.push(4);
/// ```
///
/// [`reserve`]: BinaryHeap::reserve
#[stable(feature = "rust1", since = "1.0.0")]
pub fn reserve_exact(&mut self, additional: usize) {
self.data.reserve_exact(additional);
}
/// Reserves capacity for at least `additional` elements more than the
/// current length. The allocator may reserve more space to speculatively
/// avoid frequent allocations. After calling `reserve`,
/// capacity will be greater than or equal to `self.len() + additional`.
/// Does nothing if capacity is already sufficient.
///
/// # Panics
///
/// Panics if the new capacity overflows [`usize`].
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// let mut heap = BinaryHeap::new();
/// heap.reserve(100);
/// assert!(heap.capacity() >= 100);
/// heap.push(4);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn reserve(&mut self, additional: usize) {
self.data.reserve(additional);
}
/// Tries to reserve the minimum capacity for at least `additional` elements
/// more than the current length. Unlike [`try_reserve`], this will not
/// deliberately over-allocate to speculatively avoid frequent allocations.
/// After calling `try_reserve_exact`, capacity will be greater than or
/// equal to `self.len() + additional` if it returns `Ok(())`.
/// Does nothing if the capacity is already sufficient.
///
/// Note that the allocator may give the collection more space than it
/// requests. Therefore, capacity can not be relied upon to be precisely
/// minimal. Prefer [`try_reserve`] if future insertions are expected.
///
/// [`try_reserve`]: BinaryHeap::try_reserve
///
/// # Errors
///
/// If the capacity overflows, or the allocator reports a failure, then an error
/// is returned.
///
/// # Examples
///
/// ```
/// use std::collections::BinaryHeap;
/// use std::collections::TryReserveError;
///
/// fn find_max_slow(data: &[u32]) -> Result<Option<u32>, TryReserveError> {
/// let mut heap = BinaryHeap::new();
///
/// // Pre-reserve the memory, exiting if we can't
/// heap.try_reserve_exact(data.len())?;
///
/// // Now we know this can't OOM in the middle of our complex work
/// heap.extend(data.iter());
///
/// Ok(heap.pop())
/// }
/// # find_max_slow(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
/// ```
#[stable(feature = "try_reserve_2", since = "1.63.0")]
pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
self.data.try_reserve_exact(additional)
}
/// Tries to reserve capacity for at least `additional` elements more than the
/// current length. The allocator may reserve more space to speculatively
/// avoid frequent allocations. After calling `try_reserve`, capacity will be
/// greater than or equal to `self.len() + additional` if it returns
/// `Ok(())`. Does nothing if capacity is already sufficient. This method
/// preserves the contents even if an error occurs.
///
/// # Errors
///
/// If the capacity overflows, or the allocator reports a failure, then an error
/// is returned.
///
/// # Examples
///
/// ```
/// use std::collections::BinaryHeap;
/// use std::collections::TryReserveError;
///
/// fn find_max_slow(data: &[u32]) -> Result<Option<u32>, TryReserveError> {
/// let mut heap = BinaryHeap::new();
///
/// // Pre-reserve the memory, exiting if we can't
/// heap.try_reserve(data.len())?;
///
/// // Now we know this can't OOM in the middle of our complex work
/// heap.extend(data.iter());
///
/// Ok(heap.pop())
/// }
/// # find_max_slow(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
/// ```
#[stable(feature = "try_reserve_2", since = "1.63.0")]
pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
self.data.try_reserve(additional)
}
/// Discards as much additional capacity as possible.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// let mut heap: BinaryHeap<i32> = BinaryHeap::with_capacity(100);
///
/// assert!(heap.capacity() >= 100);
/// heap.shrink_to_fit();
/// assert!(heap.capacity() == 0);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn shrink_to_fit(&mut self) {
self.data.shrink_to_fit();
}
/// Discards capacity with a lower bound.
///
/// The capacity will remain at least as large as both the length
/// and the supplied value.
///
/// If the current capacity is less than the lower limit, this is a no-op.
///
/// # Examples
///
/// ```
/// use std::collections::BinaryHeap;
/// let mut heap: BinaryHeap<i32> = BinaryHeap::with_capacity(100);
///
/// assert!(heap.capacity() >= 100);
/// heap.shrink_to(10);
/// assert!(heap.capacity() >= 10);
/// ```
#[inline]
#[stable(feature = "shrink_to", since = "1.56.0")]
pub fn shrink_to(&mut self, min_capacity: usize) {
self.data.shrink_to(min_capacity)
}
/// Returns a slice of all values in the underlying vector, in arbitrary
/// order.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// use std::io::{self, Write};
///
/// let heap = BinaryHeap::from([1, 2, 3, 4, 5, 6, 7]);
///
/// io::sink().write(heap.as_slice()).unwrap();
/// ```
#[must_use]
#[stable(feature = "binary_heap_as_slice", since = "1.80.0")]
pub fn as_slice(&self) -> &[T] {
self.data.as_slice()
}
/// Consumes the `BinaryHeap` and returns the underlying vector
/// in arbitrary order.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// let heap = BinaryHeap::from([1, 2, 3, 4, 5, 6, 7]);
/// let vec = heap.into_vec();
///
/// // Will print in some order
/// for x in vec {
/// println!("{x}");
/// }
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "binary_heap_extras_15", since = "1.5.0")]
pub fn into_vec(self) -> Vec<T, A> {
self.into()
}
/// Returns a reference to the underlying allocator.
#[unstable(feature = "allocator_api", issue = "32838")]
#[inline]
pub fn allocator(&self) -> &A {
self.data.allocator()
}
/// Returns the length of the binary heap.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// let heap = BinaryHeap::from([1, 3]);
///
/// assert_eq!(heap.len(), 2);
/// ```
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_confusables("length", "size")]
pub fn len(&self) -> usize {
self.data.len()
}
/// Checks if the binary heap is empty.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// let mut heap = BinaryHeap::new();
///
/// assert!(heap.is_empty());
///
/// heap.push(3);
/// heap.push(5);
/// heap.push(1);
///
/// assert!(!heap.is_empty());
/// ```
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn is_empty(&self) -> bool {
self.len() == 0
}
/// Clears the binary heap, returning an iterator over the removed elements
/// in arbitrary order. If the iterator is dropped before being fully
/// consumed, it drops the remaining elements in arbitrary order.
///
/// The returned iterator keeps a mutable borrow on the heap to optimize
/// its implementation.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// let mut heap = BinaryHeap::from([1, 3]);
///
/// assert!(!heap.is_empty());
///
/// for x in heap.drain() {
/// println!("{x}");
/// }
///
/// assert!(heap.is_empty());
/// ```
#[inline]
#[stable(feature = "drain", since = "1.6.0")]
pub fn drain(&mut self) -> Drain<'_, T, A> {
Drain { iter: self.data.drain(..) }
}
/// Drops all items from the binary heap.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// let mut heap = BinaryHeap::from([1, 3]);
///
/// assert!(!heap.is_empty());
///
/// heap.clear();
///
/// assert!(heap.is_empty());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn clear(&mut self) {
self.drain();
}
}
/// Hole represents a hole in a slice i.e., an index without valid value
/// (because it was moved from or duplicated).
/// In drop, `Hole` will restore the slice by filling the hole
/// position with the value that was originally removed.
struct Hole<'a, T: 'a> {
data: &'a mut [T],
elt: ManuallyDrop<T>,
pos: usize,
}
impl<'a, T> Hole<'a, T> {
/// Create a new `Hole` at index `pos`.
///
/// Unsafe because pos must be within the data slice.
#[inline]
unsafe fn new(data: &'a mut [T], pos: usize) -> Self {
debug_assert!(pos < data.len());
// SAFE: pos should be inside the slice
let elt = unsafe { ptr::read(data.get_unchecked(pos)) };
Hole { data, elt: ManuallyDrop::new(elt), pos }
}
#[inline]
fn pos(&self) -> usize {
self.pos
}
/// Returns a reference to the element removed.
#[inline]
fn element(&self) -> &T {
&self.elt
}
/// Returns a reference to the element at `index`.
///
/// Unsafe because index must be within the data slice and not equal to pos.
#[inline]
unsafe fn get(&self, index: usize) -> &T {
debug_assert!(index != self.pos);
debug_assert!(index < self.data.len());
unsafe { self.data.get_unchecked(index) }
}
/// Move hole to new location
///
/// Unsafe because index must be within the data slice and not equal to pos.
#[inline]
unsafe fn move_to(&mut self, index: usize) {
debug_assert!(index != self.pos);
debug_assert!(index < self.data.len());
unsafe {
let ptr = self.data.as_mut_ptr();
let index_ptr: *const _ = ptr.add(index);
let hole_ptr = ptr.add(self.pos);
ptr::copy_nonoverlapping(index_ptr, hole_ptr, 1);
}
self.pos = index;
}
}
impl<T> Drop for Hole<'_, T> {
#[inline]
fn drop(&mut self) {
// fill the hole again
unsafe {
let pos = self.pos;
ptr::copy_nonoverlapping(&*self.elt, self.data.get_unchecked_mut(pos), 1);
}
}
}
/// An iterator over the elements of a `BinaryHeap`.
///
/// This `struct` is created by [`BinaryHeap::iter()`]. See its
/// documentation for more.
///
/// [`iter`]: BinaryHeap::iter
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Iter<'a, T: 'a> {
iter: slice::Iter<'a, T>,
}
#[stable(feature = "collection_debug", since = "1.17.0")]
impl<T: fmt::Debug> fmt::Debug for Iter<'_, T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_tuple("Iter").field(&self.iter.as_slice()).finish()
}
}
// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> Clone for Iter<'_, T> {
fn clone(&self) -> Self {
Iter { iter: self.iter.clone() }
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, T> Iterator for Iter<'a, T> {
type Item = &'a T;
#[inline]
fn next(&mut self) -> Option<&'a T> {
self.iter.next()
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
#[inline]
fn last(self) -> Option<&'a T> {
self.iter.last()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
#[inline]
fn next_back(&mut self) -> Option<&'a T> {
self.iter.next_back()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> ExactSizeIterator for Iter<'_, T> {
fn is_empty(&self) -> bool {
self.iter.is_empty()
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl<T> FusedIterator for Iter<'_, T> {}
/// An owning iterator over the elements of a `BinaryHeap`.
///
/// This `struct` is created by [`BinaryHeap::into_iter()`]
/// (provided by the [`IntoIterator`] trait). See its documentation for more.
///
/// [`into_iter`]: BinaryHeap::into_iter
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct IntoIter<
T,
#[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
> {
iter: vec::IntoIter<T, A>,
}
impl<T, A: Allocator> IntoIter<T, A> {
/// Returns a reference to the underlying allocator.
#[unstable(feature = "allocator_api", issue = "32838")]
pub fn allocator(&self) -> &A {
self.iter.allocator()
}
}
#[stable(feature = "collection_debug", since = "1.17.0")]
impl<T: fmt::Debug, A: Allocator> fmt::Debug for IntoIter<T, A> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_tuple("IntoIter").field(&self.iter.as_slice()).finish()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T, A: Allocator> Iterator for IntoIter<T, A> {
type Item = T;
#[inline]
fn next(&mut self) -> Option<T> {
self.iter.next()
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
#[inline]
fn next_back(&mut self) -> Option<T> {
self.iter.next_back()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T, A: Allocator> ExactSizeIterator for IntoIter<T, A> {
fn is_empty(&self) -> bool {
self.iter.is_empty()
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl<T, A: Allocator> FusedIterator for IntoIter<T, A> {}
#[doc(hidden)]
#[unstable(issue = "none", feature = "trusted_fused")]
unsafe impl<T, A: Allocator> TrustedFused for IntoIter<T, A> {}
#[stable(feature = "default_iters", since = "1.70.0")]
impl<T> Default for IntoIter<T> {
/// Creates an empty `binary_heap::IntoIter`.
///
/// ```
/// # use std::collections::binary_heap;
/// let iter: binary_heap::IntoIter<u8> = Default::default();
/// assert_eq!(iter.len(), 0);
/// ```
fn default() -> Self {
IntoIter { iter: Default::default() }
}
}
// In addition to the SAFETY invariants of the following three unsafe traits
// also refer to the vec::in_place_collect module documentation to get an overview
#[unstable(issue = "none", feature = "inplace_iteration")]
#[doc(hidden)]
unsafe impl<T, A: Allocator> SourceIter for IntoIter<T, A> {
type Source = IntoIter<T, A>;
#[inline]
unsafe fn as_inner(&mut self) -> &mut Self::Source {
self
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
#[doc(hidden)]
unsafe impl<I, A: Allocator> InPlaceIterable for IntoIter<I, A> {
const EXPAND_BY: Option<NonZero<usize>> = NonZero::new(1);
const MERGE_BY: Option<NonZero<usize>> = NonZero::new(1);
}
unsafe impl<I> AsVecIntoIter for IntoIter<I> {
type Item = I;
fn as_into_iter(&mut self) -> &mut vec::IntoIter<Self::Item> {
&mut self.iter
}
}
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[unstable(feature = "binary_heap_into_iter_sorted", issue = "59278")]
#[derive(Clone, Debug)]
pub struct IntoIterSorted<
T,
#[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
> {
inner: BinaryHeap<T, A>,
}
impl<T, A: Allocator> IntoIterSorted<T, A> {
/// Returns a reference to the underlying allocator.
#[unstable(feature = "allocator_api", issue = "32838")]
pub fn allocator(&self) -> &A {
self.inner.allocator()
}
}
#[unstable(feature = "binary_heap_into_iter_sorted", issue = "59278")]
impl<T: Ord, A: Allocator> Iterator for IntoIterSorted<T, A> {
type Item = T;
#[inline]
fn next(&mut self) -> Option<T> {
self.inner.pop()
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let exact = self.inner.len();
(exact, Some(exact))
}
}
#[unstable(feature = "binary_heap_into_iter_sorted", issue = "59278")]
impl<T: Ord, A: Allocator> ExactSizeIterator for IntoIterSorted<T, A> {}
#[unstable(feature = "binary_heap_into_iter_sorted", issue = "59278")]
impl<T: Ord, A: Allocator> FusedIterator for IntoIterSorted<T, A> {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<T: Ord, A: Allocator> TrustedLen for IntoIterSorted<T, A> {}
/// A draining iterator over the elements of a `BinaryHeap`.
///
/// This `struct` is created by [`BinaryHeap::drain()`]. See its
/// documentation for more.
///
/// [`drain`]: BinaryHeap::drain
#[stable(feature = "drain", since = "1.6.0")]
#[derive(Debug)]
pub struct Drain<
'a,
T: 'a,
#[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
> {
iter: vec::Drain<'a, T, A>,
}
impl<T, A: Allocator> Drain<'_, T, A> {
/// Returns a reference to the underlying allocator.
#[unstable(feature = "allocator_api", issue = "32838")]
pub fn allocator(&self) -> &A {
self.iter.allocator()
}
}
#[stable(feature = "drain", since = "1.6.0")]
impl<T, A: Allocator> Iterator for Drain<'_, T, A> {
type Item = T;
#[inline]
fn next(&mut self) -> Option<T> {
self.iter.next()
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
}
#[stable(feature = "drain", since = "1.6.0")]
impl<T, A: Allocator> DoubleEndedIterator for Drain<'_, T, A> {
#[inline]
fn next_back(&mut self) -> Option<T> {
self.iter.next_back()
}
}
#[stable(feature = "drain", since = "1.6.0")]
impl<T, A: Allocator> ExactSizeIterator for Drain<'_, T, A> {
fn is_empty(&self) -> bool {
self.iter.is_empty()
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl<T, A: Allocator> FusedIterator for Drain<'_, T, A> {}
/// A draining iterator over the elements of a `BinaryHeap`.
///
/// This `struct` is created by [`BinaryHeap::drain_sorted()`]. See its
/// documentation for more.
///
/// [`drain_sorted`]: BinaryHeap::drain_sorted
#[unstable(feature = "binary_heap_drain_sorted", issue = "59278")]
#[derive(Debug)]
pub struct DrainSorted<
'a,
T: Ord,
#[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
> {
inner: &'a mut BinaryHeap<T, A>,
}
impl<'a, T: Ord, A: Allocator> DrainSorted<'a, T, A> {
/// Returns a reference to the underlying allocator.
#[unstable(feature = "allocator_api", issue = "32838")]
pub fn allocator(&self) -> &A {
self.inner.allocator()
}
}
#[unstable(feature = "binary_heap_drain_sorted", issue = "59278")]
impl<'a, T: Ord, A: Allocator> Drop for DrainSorted<'a, T, A> {
/// Removes heap elements in heap order.
fn drop(&mut self) {
struct DropGuard<'r, 'a, T: Ord, A: Allocator>(&'r mut DrainSorted<'a, T, A>);
impl<'r, 'a, T: Ord, A: Allocator> Drop for DropGuard<'r, 'a, T, A> {
fn drop(&mut self) {
while self.0.inner.pop().is_some() {}
}
}
while let Some(item) = self.inner.pop() {
let guard = DropGuard(self);
drop(item);
mem::forget(guard);
}
}
}
#[unstable(feature = "binary_heap_drain_sorted", issue = "59278")]
impl<T: Ord, A: Allocator> Iterator for DrainSorted<'_, T, A> {
type Item = T;
#[inline]
fn next(&mut self) -> Option<T> {
self.inner.pop()
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let exact = self.inner.len();
(exact, Some(exact))
}
}
#[unstable(feature = "binary_heap_drain_sorted", issue = "59278")]
impl<T: Ord, A: Allocator> ExactSizeIterator for DrainSorted<'_, T, A> {}
#[unstable(feature = "binary_heap_drain_sorted", issue = "59278")]
impl<T: Ord, A: Allocator> FusedIterator for DrainSorted<'_, T, A> {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<T: Ord, A: Allocator> TrustedLen for DrainSorted<'_, T, A> {}
#[stable(feature = "binary_heap_extras_15", since = "1.5.0")]
impl<T: Ord, A: Allocator> From<Vec<T, A>> for BinaryHeap<T, A> {
/// Converts a `Vec<T>` into a `BinaryHeap<T>`.
///
/// This conversion happens in-place, and has *O*(*n*) time complexity.
fn from(vec: Vec<T, A>) -> BinaryHeap<T, A> {
let mut heap = BinaryHeap { data: vec };
heap.rebuild();
heap
}
}
#[stable(feature = "std_collections_from_array", since = "1.56.0")]
impl<T: Ord, const N: usize> From<[T; N]> for BinaryHeap<T> {
/// ```
/// use std::collections::BinaryHeap;
///
/// let mut h1 = BinaryHeap::from([1, 4, 2, 3]);
/// let mut h2: BinaryHeap<_> = [1, 4, 2, 3].into();
/// while let Some((a, b)) = h1.pop().zip(h2.pop()) {
/// assert_eq!(a, b);
/// }
/// ```
fn from(arr: [T; N]) -> Self {
Self::from_iter(arr)
}
}
#[stable(feature = "binary_heap_extras_15", since = "1.5.0")]
impl<T, A: Allocator> From<BinaryHeap<T, A>> for Vec<T, A> {
/// Converts a `BinaryHeap<T>` into a `Vec<T>`.
///
/// This conversion requires no data movement or allocation, and has
/// constant time complexity.
fn from(heap: BinaryHeap<T, A>) -> Vec<T, A> {
heap.data
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Ord> FromIterator<T> for BinaryHeap<T> {
fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> BinaryHeap<T> {
BinaryHeap::from(iter.into_iter().collect::<Vec<_>>())
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T, A: Allocator> IntoIterator for BinaryHeap<T, A> {
type Item = T;
type IntoIter = IntoIter<T, A>;
/// Creates a consuming iterator, that is, one that moves each value out of
/// the binary heap in arbitrary order. The binary heap cannot be used
/// after calling this.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::collections::BinaryHeap;
/// let heap = BinaryHeap::from([1, 2, 3, 4]);
///
/// // Print 1, 2, 3, 4 in arbitrary order
/// for x in heap.into_iter() {
/// // x has type i32, not &i32
/// println!("{x}");
/// }
/// ```
fn into_iter(self) -> IntoIter<T, A> {
IntoIter { iter: self.data.into_iter() }
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, T, A: Allocator> IntoIterator for &'a BinaryHeap<T, A> {
type Item = &'a T;
type IntoIter = Iter<'a, T>;
fn into_iter(self) -> Iter<'a, T> {
self.iter()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Ord, A: Allocator> Extend<T> for BinaryHeap<T, A> {
#[inline]
fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
let guard = RebuildOnDrop { rebuild_from: self.len(), heap: self };
guard.heap.data.extend(iter);
}
#[inline]
fn extend_one(&mut self, item: T) {
self.push(item);
}
#[inline]
fn extend_reserve(&mut self, additional: usize) {
self.reserve(additional);
}
}
#[stable(feature = "extend_ref", since = "1.2.0")]
impl<'a, T: 'a + Ord + Copy, A: Allocator> Extend<&'a T> for BinaryHeap<T, A> {
fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
self.extend(iter.into_iter().cloned());
}
#[inline]
fn extend_one(&mut self, &item: &'a T) {
self.push(item);
}
#[inline]
fn extend_reserve(&mut self, additional: usize) {
self.reserve(additional);
}
}