Struct alloc::collections::binary_heap::BinaryHeap

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

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>

pub fn new() -> 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);

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

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>>

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>

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)

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>

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)

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>

Important traits for Iter<'a, T>

impl<'a, T> Iterator for Iter<'a, T> type Item = &'a T;

pub fn iter(&self) -> Iter<T>

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>

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

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)

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)

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)

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)

🔬 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>

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

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

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>

impl<T, '_> Iterator for Drain<'_, T> type Item = T;

pub fn drain(&mut self) -> Drain<T>

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)

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: Ord> From<Vec<T>> for BinaryHeap<T>

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

Performs the conversion.

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

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

Performs the conversion.

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

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

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

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

Extends a collection with the contents of an iterator.

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

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

Extends a collection with the contents of an iterator.

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

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

Creates a value from an iterator.

impl<T> IntoIterator for BinaryHeap<T>

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>

impl<T> Iterator for IntoIter<T> type Item = T;

fn into_iter(self) -> IntoIter<T>

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>

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>

impl<'a, T> Iterator for Iter<'a, T> type Item = &'a T;

fn into_iter(self) -> Iter<'a, T>

Creates an iterator from a value.

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

fn clone(&self) -> Self

Returns a copy of the value.

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

Performs copy-assignment from source.

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

fn default() -> BinaryHeap<T>

Creates an empty BinaryHeap<T>.