# 1.0.0[−][src]Struct alloc::collections::binary_heap::BinaryHeap

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.

# 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())

## 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);

# 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.

## Methods

`impl<T: Ord> BinaryHeap<T>`

[src]

`pub fn new() -> BinaryHeap<T>`

[src]

Creates an empty `BinaryHeap`

as a max-heap.

# Examples

Basic usage:

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

`pub fn with_capacity(capacity: usize) -> BinaryHeap<T>`

[src]

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);

`pub fn peek_mut(&mut self) -> Option<PeekMut<T>>`

1.12.0[src]

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));

# Time complexity

Cost is O(1) in the worst case.

`pub fn pop(&mut self) -> Option<T>`

[src]

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);

# Time complexity

The worst case cost of `pop`

on a heap containing *n* elements is O(log
n).

`pub fn push(&mut self, item: T)`

[src]

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.

`pub fn into_sorted_vec(self) -> Vec<T>`

1.5.0[src]

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]);

`pub fn append(&mut self, other: &mut Self)`

1.11.0[src]

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());

`impl<T> BinaryHeap<T>`

[src]

#### ⓘImportant traits for Iter<'a, T>`pub fn iter(&self) -> Iter<T>`

[src]

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); }

`pub fn peek(&self) -> Option<&T>`

[src]

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.

`pub fn capacity(&self) -> usize`

[src]

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);

`pub fn reserve_exact(&mut self, additional: usize)`

[src]

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);

`pub fn reserve(&mut self, additional: usize)`

[src]

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);

`pub fn shrink_to_fit(&mut self)`

[src]

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);

`pub fn shrink_to(&mut self, min_capacity: usize)`

[src]

## 🔬 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.

Panics if the current capacity is smaller than the supplied minimum capacity.

# 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);

`pub fn into_vec(self) -> Vec<T>`

1.5.0[src]

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); }

`pub fn len(&self) -> usize`

[src]

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);

`pub fn is_empty(&self) -> bool`

[src]

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());

#### ⓘImportant traits for Drain<'_, T>`pub fn drain(&mut self) -> Drain<T>`

1.6.0[src]

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());

`pub fn clear(&mut self)`

[src]

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());

## Trait Implementations

`impl<T: Debug> Debug for BinaryHeap<T>`

1.4.0[src]

`impl<T> IntoIterator for BinaryHeap<T>`

[src]

`type Item = T`

The type of the elements being iterated over.

`type IntoIter = IntoIter<T>`

Which kind of iterator are we turning this into?

#### ⓘImportant traits for IntoIter<T>`fn into_iter(self) -> IntoIter<T>`

[src]

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); }

`impl<'a, T> IntoIterator for &'a BinaryHeap<T>`

[src]

`type Item = &'a T`

The type of the elements being iterated over.

`type IntoIter = Iter<'a, T>`

Which kind of iterator are we turning this into?

#### ⓘImportant traits for Iter<'a, T>`fn into_iter(self) -> Iter<'a, T>`

[src]

`impl<T: Ord> Extend<T> for BinaryHeap<T>`

[src]

`fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I)`

[src]

`impl<'a, T: 'a + Ord + Copy> Extend<&'a T> for BinaryHeap<T>`

1.2.0[src]

`fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I)`

[src]

`impl<T: Ord> FromIterator<T> for BinaryHeap<T>`

[src]

`fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> BinaryHeap<T>`

[src]

`impl<T: Ord> From<Vec<T>> for BinaryHeap<T>`

1.5.0[src]

`fn from(vec: Vec<T>) -> BinaryHeap<T>`

[src]

`impl<T> From<BinaryHeap<T>> for Vec<T>`

1.5.0[src]

`fn from(heap: BinaryHeap<T>) -> Vec<T>`

[src]

`impl<T: Clone> Clone for BinaryHeap<T>`

[src]

`fn clone(&self) -> Self`

[src]

`fn clone_from(&mut self, source: &Self)`

[src]

`impl<T: Ord> Default for BinaryHeap<T>`

[src]

`fn default() -> BinaryHeap<T>`

[src]

Creates an empty `BinaryHeap<T>`

.

## Auto Trait Implementations

`impl<T> Unpin for BinaryHeap<T> where`

T: Unpin,

T: Unpin,

`impl<T> Send for BinaryHeap<T> where`

T: Send,

T: Send,

`impl<T> Sync for BinaryHeap<T> where`

T: Sync,

T: Sync,

## Blanket Implementations

`impl<T> ToOwned for T where`

T: Clone,

[src]

T: Clone,

`type Owned = T`

The resulting type after obtaining ownership.

`fn to_owned(&Self) -> T`

[src]

`fn clone_into(&Self, &mut T)`

[src]

`impl<T, U> TryFrom<U> for T where`

U: Into<T>,

[src]

U: Into<T>,

`type Error = Infallible`

The type returned in the event of a conversion error.

`fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>`

[src]

`impl<I> IntoIterator for I where`

I: Iterator,

[src]

I: Iterator,

`type Item = <I as Iterator>::Item`

The type of the elements being iterated over.

`type IntoIter = I`

Which kind of iterator are we turning this into?

`fn into_iter(self) -> I`

[src]

`impl<T, U> Into<U> for T where`

U: From<T>,

[src]

U: From<T>,

`impl<T> From<T> for T`

[src]

`impl<T, U> TryInto<U> for T where`

U: TryFrom<T>,

[src]

U: TryFrom<T>,

`type Error = <U as TryFrom<T>>::Error`

The type returned in the event of a conversion error.

`fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>`

[src]

`impl<T> Borrow<T> for T where`

T: ?Sized,

[src]

T: ?Sized,

`impl<T> BorrowMut<T> for T where`

T: ?Sized,

[src]

T: ?Sized,

`fn borrow_mut(&mut self) -> &mut T`

[src]

`impl<T> Any for T where`

T: 'static + ?Sized,

[src]

T: 'static + ?Sized,