# Struct std::collections::BinaryHeap 1.0.0[−][src]

## 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())
```

RunA `BinaryHeap`

with a known list of items can be initialized from an array:

```
use std::collections::BinaryHeap;
let heap = BinaryHeap::from([1, 5, 2]);
```

Run### 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);
```

Run## Time complexity

The value for `push`

is an expected cost; the method documentation gives a
more detailed analysis.

## Fields

`data: Vec<T, Global>`

## Implementations

## This is supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

## This is supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

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## This is supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

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).

## This is supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

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*)).

## This is supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

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.

## This is supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

## This is supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

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#### pub fn drain_sorted(&mut self) -> DrainSorted<'_, T>ⓘNotable traits for DrainSorted<'_, T>`impl<'_, T> Iterator for DrainSorted<'_, T> where`

T: Ord, type Item = T;

This is supported on **non-**`no_global_oom_handling`

only.

#### pub fn drain_sorted(&mut self) -> DrainSorted<'_, T>ⓘNotable traits for DrainSorted<'_, T>`impl<'_, T> Iterator for DrainSorted<'_, T> where`

T: Ord, type Item = T;

`impl<'_, T> Iterator for DrainSorted<'_, T> where`

T: Ord, type Item = T;

**non-**only.

`no_global_oom_handling`

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 supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

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#### pub fn into_iter_sorted(self) -> IntoIterSorted<T>ⓘNotable traits for IntoIterSorted<T>`impl<T> Iterator for IntoIterSorted<T> where`

T: Ord, type Item = T;

This is supported on **non-**`no_global_oom_handling`

only.

#### pub fn into_iter_sorted(self) -> IntoIterSorted<T>ⓘNotable traits for IntoIterSorted<T>`impl<T> Iterator for IntoIterSorted<T> where`

T: Ord, type Item = T;

`impl<T> Iterator for IntoIterSorted<T> where`

T: Ord, type Item = T;

**non-**only.

`no_global_oom_handling`

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## This is supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

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.

## This is supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

## This is supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

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## This is supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

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## This is supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

## This is supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

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);
```

Run## This is supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

## This is supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

## This is supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

## This is supported on **non-**`no_global_oom_handling`

only.

**non-**only.

`no_global_oom_handling`

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## Trait Implementations

Creates an empty `BinaryHeap<T>`

.

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#### type Item = T

#### type Item = T

The type of the elements being iterated over.

## Auto Trait Implementations

### impl<T> RefUnwindSafe for BinaryHeap<T> where

T: RefUnwindSafe,

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

T: Send,

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

T: Sync,

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

T: Unpin,

### impl<T> UnwindSafe for BinaryHeap<T> where

T: UnwindSafe,

## Blanket Implementations

Mutably borrows from an owned value. Read more