Struct BinaryHeap

struct BinaryHeap<T, A: Allocator = crate::alloc::Global> { ... }

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.

Implementations

impl<T> BinaryHeap<T>

const 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);

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

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 zero, the binary heap will not allocate.

Examples

Basic usage:

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

impl<T, A: Allocator> BinaryHeap<T, A>

fn iter(self: &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([1, 2, 3, 4]);

// Print 1, 2, 3, 4 in arbitrary order
for x in heap.iter() {
    println!("{x}");
}

fn into_iter_sorted(self: Self) -> IntoIterSorted<T, A>

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]);

fn peek(self: &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.

fn capacity(self: &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);

fn reserve_exact(self: &mut Self, additional: usize)

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.

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);

fn reserve(self: &mut Self, additional: usize)

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);

fn try_reserve_exact(self: &mut Self, additional: usize) -> Result<(), TryReserveError>

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.

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?");

fn try_reserve(self: &mut Self, additional: usize) -> Result<(), TryReserveError>

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?");

fn shrink_to_fit(self: &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);

fn shrink_to(self: &mut Self, min_capacity: usize)

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);

fn as_slice(self: &Self) -> &[T]

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();

fn into_vec(self: Self) -> Vec<T, A>

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}");
}

fn allocator(self: &Self) -> &A

Returns a reference to the underlying allocator.

fn len(self: &Self) -> usize

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);

fn is_empty(self: &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());

fn drain(self: &mut Self) -> Drain<'_, T, A>

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());

fn clear(self: &mut Self)

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());

impl<T, A: Allocator> BinaryHeap<T, A>

const fn new_in(alloc: A) -> 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);

fn with_capacity_in(capacity: usize, alloc: A) -> BinaryHeap<T, A>

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 zero, 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);

impl<T: Ord, A: Allocator> BinaryHeap<T, A>

fn peek_mut(self: &mut Self) -> Option<PeekMut<'_, T, A>>

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);
if let Some(mut val) = heap.peek_mut() {
    *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).

fn pop(self: &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([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)).

fn push(self: &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.

fn into_sorted_vec(self: Self) -> Vec<T, A>

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]);

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

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());

fn drain_sorted(self: &mut Self) -> DrainSorted<'_, T, A>

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);

fn retain<F>(self: &mut Self, f: F)
where
    F: FnMut(&T) -> bool

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])

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

fn extend<I: IntoIterator<Item = &'a T>>(self: &mut Self, iter: I)
fn extend_one(self: &mut Self, item: &'a T)
fn extend_reserve(self: &mut Self, additional: usize)

impl<T> Any for BinaryHeap<T, A>

fn type_id(self: &Self) -> TypeId

impl<T> Borrow for BinaryHeap<T, A>

fn borrow(self: &Self) -> &T

impl<T> BorrowMut for BinaryHeap<T, A>

fn borrow_mut(self: &mut Self) -> &mut T

impl<T> CloneToUninit for BinaryHeap<T, A>

unsafe fn clone_to_uninit(self: &Self, dest: *mut u8)

impl<T> Default for BinaryHeap<T>

fn default() -> BinaryHeap<T>

Creates an empty BinaryHeap<T>.

impl<T> From for BinaryHeap<T, A>

fn from(t: T) -> T

Returns the argument unchanged.

impl<T> ToOwned for BinaryHeap<T, A>

fn to_owned(self: &Self) -> T
fn clone_into(self: &Self, target: &mut T)

impl<T, A> Freeze for BinaryHeap<T, A>

impl<T, A> RefUnwindSafe for BinaryHeap<T, A>

impl<T, A> Send for BinaryHeap<T, A>

impl<T, A> Sync for BinaryHeap<T, A>

impl<T, A> Unpin for BinaryHeap<T, A>

impl<T, A> UnwindSafe for BinaryHeap<T, A>

impl<T, A: Allocator> IntoIterator for BinaryHeap<T, A>

fn into_iter(self: Self) -> 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}");
}

impl<T, U> Into for BinaryHeap<T, A>

fn into(self: Self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of [From]<T> for U chooses to do.

impl<T, U> TryFrom for BinaryHeap<T, A>

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

impl<T, U> TryInto for BinaryHeap<T, A>

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

impl<T: Clone, A: Allocator + Clone> Clone for BinaryHeap<T, A>

fn clone(self: &Self) -> Self
fn clone_from(self: &mut Self, source: &Self)

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.

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

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

impl<T: Ord, A: Allocator> Extend for BinaryHeap<T, A>

fn extend<I: IntoIterator<Item = T>>(self: &mut Self, iter: I)
fn extend_one(self: &mut Self, item: T)
fn extend_reserve(self: &mut Self, additional: usize)

impl<T: Ord, A: Allocator> From for BinaryHeap<T, A>

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

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

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

impl<T: Ord, N: usize> From for BinaryHeap<T>

fn from(arr: [T; N]) -> Self
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);
}

impl<T: fmt::Debug, A: Allocator> Debug for BinaryHeap<T, A>

fn fmt(self: &Self, f: &mut fmt::Formatter<'_>) -> fmt::Result