Struct alloc::collections::binary_heap::BinaryHeap1.0.0[][src]

pub struct BinaryHeap<T> { /* fields omitted */ }
Expand description

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 Cell, RefCell, global state, I/O, or unsafe code. The behavior resulting from such a logic error is not specified, but will not result in undefined behavior. This could include panics, incorrect results, aborts, memory leaks, and non-termination.

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())
Run

Min-heap

Either std::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);
Run

Time complexity

pushpoppeek/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.

Implementations

Creates an empty BinaryHeap as a max-heap.

Examples

Basic usage:

use std::collections::BinaryHeap;
let mut heap = BinaryHeap::new();
heap.push(4);
Run

Creates an empty BinaryHeap with a specific capacity. This preallocates enough memory for capacity elements, so that the BinaryHeap does not have to be reallocated until it contains at least that many values.

Examples

Basic usage:

use std::collections::BinaryHeap;
let mut heap = BinaryHeap::with_capacity(10);
heap.push(4);
Run

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, the heap may be in an inconsistent state.

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));
Run

Time complexity

If the item is modified then the worst case time complexity is O(log(n)), otherwise it’s O(1).

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(vec![1, 3]);

assert_eq!(heap.pop(), Some(3));
assert_eq!(heap.pop(), Some(1));
assert_eq!(heap.pop(), None);
Run

Time complexity

The worst case cost of pop on a heap containing n elements is O(log(n)).

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));
Run

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.

Consumes the BinaryHeap and returns a vector in sorted (ascending) order.

Examples

Basic usage:

use std::collections::BinaryHeap;

let mut heap = BinaryHeap::from(vec![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]);
Run

Moves all the elements of other into self, leaving other empty.

Examples

Basic usage:

use std::collections::BinaryHeap;

let v = vec![-10, 1, 2, 3, 3];
let mut a = BinaryHeap::from(v);

let v = vec![-20, 5, 43];
let mut b = BinaryHeap::from(v);

a.append(&mut b);

assert_eq!(a.into_sorted_vec(), [-20, -10, 1, 2, 3, 3, 5, 43]);
assert!(b.is_empty());
Run
🔬 This is a nightly-only experimental API. (binary_heap_drain_sorted #59278)

Returns an iterator which retrieves elements in heap order. The retrieved elements are removed from the original heap. The remaining elements will be removed on drop in heap order.

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(vec![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);
Run
🔬 This is a nightly-only experimental API. (binary_heap_retain #71503)

Retains only the elements specified by the predicate.

In other words, remove all elements e such that f(&e) returns false. The elements are visited in unsorted (and unspecified) order.

Examples

Basic usage:

#![feature(binary_heap_retain)]
use std::collections::BinaryHeap;

let mut heap = BinaryHeap::from(vec![-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])
Run

Returns an iterator visiting all values in the underlying vector, in arbitrary order.

Examples

Basic usage:

use std::collections::BinaryHeap;
let heap = BinaryHeap::from(vec![1, 2, 3, 4]);

// Print 1, 2, 3, 4 in arbitrary order
for x in heap.iter() {
    println!("{}", x);
}
Run
🔬 This is a nightly-only experimental API. (binary_heap_into_iter_sorted #59278)

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(vec![1, 2, 3, 4, 5]);

assert_eq!(heap.into_iter_sorted().take(2).collect::<Vec<_>>(), vec![5, 4]);
Run

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));
Run

Time complexity

Cost is O(1) in the worst case.

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);
Run

Reserves the minimum capacity for exactly additional more elements to be inserted in the given BinaryHeap. 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 reserve if future insertions are expected.

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);
Run

Reserves capacity for at least additional more elements to be inserted in the BinaryHeap. The collection may reserve more space to avoid frequent reallocations.

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);
Run

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);
Run
🔬 This is a nightly-only experimental API. (shrink_to #56431)

new API

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

#![feature(shrink_to)]
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);
Run
🔬 This is a nightly-only experimental API. (binary_heap_as_slice #83659)

Returns a slice of all values in the underlying vector, in arbitrary order.

Examples

Basic usage:

#![feature(binary_heap_as_slice)]
use std::collections::BinaryHeap;
use std::io::{self, Write};

let heap = BinaryHeap::from(vec![1, 2, 3, 4, 5, 6, 7]);

io::sink().write(heap.as_slice()).unwrap();
Run

Consumes the BinaryHeap and returns the underlying vector in arbitrary order.

Examples

Basic usage:

use std::collections::BinaryHeap;
let heap = BinaryHeap::from(vec![1, 2, 3, 4, 5, 6, 7]);
let vec = heap.into_vec();

// Will print in some order
for x in vec {
    println!("{}", x);
}
Run

Returns the length of the binary heap.

Examples

Basic usage:

use std::collections::BinaryHeap;
let heap = BinaryHeap::from(vec![1, 3]);

assert_eq!(heap.len(), 2);
Run

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());
Run

Clears the binary heap, returning an iterator over the removed elements.

The elements are removed in arbitrary order.

Examples

Basic usage:

use std::collections::BinaryHeap;
let mut heap = BinaryHeap::from(vec![1, 3]);

assert!(!heap.is_empty());

for x in heap.drain() {
    println!("{}", x);
}

assert!(heap.is_empty());
Run

Drops all items from the binary heap.

Examples

Basic usage:

use std::collections::BinaryHeap;
let mut heap = BinaryHeap::from(vec![1, 3]);

assert!(!heap.is_empty());

heap.clear();

assert!(heap.is_empty());
Run

Trait Implementations

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

Formats the value using the given formatter. Read more

Creates an empty BinaryHeap<T>.

Extends a collection with the contents of an iterator. Read more

🔬 This is a nightly-only experimental API. (extend_one #72631)

Extends a collection with exactly one element.

🔬 This is a nightly-only experimental API. (extend_one #72631)

Reserves capacity in a collection for the given number of additional elements. Read more

Extends a collection with the contents of an iterator. Read more

🔬 This is a nightly-only experimental API. (extend_one #72631)

Extends a collection with exactly one element.

🔬 This is a nightly-only experimental API. (extend_one #72631)

Reserves capacity in a collection for the given number of additional elements. Read more

Converts a BinaryHeap<T> into a Vec<T>.

This conversion requires no data movement or allocation, and has constant time complexity.

Converts a Vec<T> into a BinaryHeap<T>.

This conversion happens in-place, and has O(n) time complexity.

Creates a value from an iterator. Read more

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(vec![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);
}
Run

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

Creates an iterator from a value. Read more

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Performs the conversion.

Performs the conversion.

The resulting type after obtaining ownership.

Creates owned data from borrowed data, usually by cloning. Read more

🔬 This is a nightly-only experimental API. (toowned_clone_into #41263)

recently added

Uses borrowed data to replace owned data, usually by cloning. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.