std::collections::BinaryHeap - Rust
Description: API documentation for the Rust `BinaryHeap` struct in crate `std`.
Keywords: rust, rustlang, rust-lang, BinaryHeap

# 1.0.0[−][src]Struct std::collections::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())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

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> BinaryHeap<T> where
T: Ord,` [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);Run

#### `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);Run

#### `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));Run

# 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);Run

# 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));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.

####
ⓘImportant traits for Vec<u8>

### Important traits for Vec<u8>

`impl Write for Vec<u8>`
`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]);Run

#### `pub fn append(&mut self, other: &mut BinaryHeap<T>)`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());Run

####
ⓘImportant traits for DrainSorted<'_, T>

### Important traits for DrainSorted<'_, T>

`impl<'_, T> Iterator for DrainSorted<'_, T> where
T: Ord, type Item = T;`
`pub fn drain_sorted(&mut self) -> DrainSorted<T>`[src]

🔬 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 lg 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

### `impl<T> BinaryHeap<T>`[src]

####
ⓘImportant traits for Iter<'a, 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>`[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);
    }Run

####
ⓘImportant traits for IntoIterSorted<T>

### Important traits for IntoIterSorted<T>

`impl<T> Iterator for IntoIterSorted<T> where
T: Ord, type Item = T;`
`pub fn into_iter_sorted(self) -> IntoIterSorted<T>`[src]

🔬 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

#### `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));
    Run

# 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);Run

#### `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);Run

#### `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);Run

#### `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);Run

#### `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);Run

####
ⓘImportant traits for Vec<u8>

### Important traits for Vec<u8>

`impl Write for Vec<u8>`
`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);
    }Run

#### `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);Run

#### `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());Run

####
ⓘImportant traits for Drain<'_, T>

### Important traits for Drain<'_, T>

`impl<'_, T> Iterator for Drain<'_, T> type Item = 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());Run

#### `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());Run

## Trait Implementations

### `impl<T> From<Vec<T>> for BinaryHeap<T> where
T: Ord,` 1.5.0[src]

#### `fn from(vec: Vec<T>) -> BinaryHeap<T>`[src]

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

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

### `impl<T> From<BinaryHeap<T>> for Vec<T>`1.5.0[src]

####
ⓘImportant traits for Vec<u8>

### Important traits for Vec<u8>

`impl Write for Vec<u8>`
`fn from(heap: BinaryHeap<T>) -> Vec<T>`[src]

Performs the conversion.

### `impl<'a, T> Extend<&'a T> for BinaryHeap<T> where
T: 'a + Copy + Ord,` 1.2.0[src]

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

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

### `impl<T> Extend<T> for BinaryHeap<T> where
T: Ord,` [src]

#### `fn extend<I>(&mut self, iter: I) where
I: IntoIterator<Item = T>,` [src]

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

### `impl<T> Default for BinaryHeap<T> where
T: Ord,` [src]

#### `fn default() -> BinaryHeap<T>`[src]

Creates an empty `BinaryHeap<T>`.

### `impl<T> Debug for BinaryHeap<T> where
T: Debug,` 1.4.0[src]

#### `fn fmt(&self, f: &mut Formatter) -> Result<(), Error>`[src]

Formats the value using the given formatter. Read more

### `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>

### Important traits for IntoIter<T>

`impl<T> Iterator for IntoIter<T> type Item = 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);
    }Run

### `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>

### 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>`[src]

Creates an iterator from a value. Read more

### `impl<T> Clone for BinaryHeap<T> where
T: Clone,` [src]

#### `fn clone(&self) -> BinaryHeap<T>`[src]

Returns a copy of the value. Read more

#### `fn clone_from(&mut self, source: &BinaryHeap<T>)`[src]

Performs copy-assignment from `source`. Read more

### `impl<T> FromIterator<T> for BinaryHeap<T> where
T: Ord,` [src]

#### `fn from_iter<I>(iter: I) -> BinaryHeap<T> where
I: IntoIterator<Item = T>,` [src]

Creates a value from an iterator. Read more

## Auto Trait Implementations

### `impl<T> UnwindSafe for BinaryHeap<T> where
T: UnwindSafe,`

### `impl<T> RefUnwindSafe for BinaryHeap<T> where
T: RefUnwindSafe,`

### `impl<T> Unpin for BinaryHeap<T> where
T: Unpin,`

### `impl<T> Send for BinaryHeap<T> where
T: Send,`

### `impl<T> Sync for BinaryHeap<T> where
T: Sync,`

## Blanket Implementations

### `impl<T> From<T> for T`[src]

#### `fn from(t: T) -> T`[src]

Performs the conversion.

### `impl<T, U> TryFrom<U> for T where
U: Into<T>,` [src]

#### `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]

Performs the conversion.

### `impl<I> IntoIterator for I where
I: Iterator,` [src]

#### `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]

Creates an iterator from a value. Read more

### `impl<T, U> Into<U> for T where
U: From<T>,` [src]

#### `fn into(self) -> U`[src]

Performs the conversion.

### `impl<T, U> TryInto<U> for T where
U: TryFrom<T>,` [src]

#### `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]

Performs the conversion.

### `impl<T> Borrow<T> for T where
T: ?Sized,` [src]

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<'_, R: Read + ?Sized> Read for &'_ mut Rimpl<'_, W: Write + ?Sized> Write for &'_ mut W`
`fn borrow(&self) -> &T`[src]

Immutably borrows from an owned value. Read more

### `impl<T> BorrowMut<T> for T where
T: ?Sized,` [src]

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<'_, R: Read + ?Sized> Read for &'_ mut Rimpl<'_, W: Write + ?Sized> Write for &'_ mut W`
`fn borrow_mut(&mut self) -> &mut T`[src]

Mutably borrows from an owned value. Read more

### `impl<T> Any for T where
T: 'static + ?Sized,` [src]

#### `fn type_id(&self) -> TypeId`[src]

Gets the `TypeId` of `self`. Read more

### `impl<T> ToOwned for T where
T: Clone,` [src]

#### `type Owned = T`

The resulting type after obtaining ownership.

#### `fn to_owned(&self) -> T`[src]

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

#### `fn clone_into(&self, target: &mut T)`[src]

🔬 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