Struct BinaryHeap

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pub struct BinaryHeap<T, K, const N: usize> { /* private fields */ }

Expand description

A priority queue implemented with a binary heap.

This can be either a min-heap or 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.

use heapless::binary_heap::{BinaryHeap, Max};

let mut heap: BinaryHeap<_, Max, 8> = 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).unwrap();
heap.push(5).unwrap();
heap.push(2).unwrap();

// 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())

Implementations§

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impl<T, K, const N: usize> BinaryHeap<T, K, N>

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pub const fn new() -> Self

Creates an empty BinaryHeap as a $K-heap.

use heapless::binary_heap::{BinaryHeap, Max};

// allocate the binary heap on the stack
let mut heap: BinaryHeap<_, Max, 8> = BinaryHeap::new();
heap.push(4).unwrap();

// allocate the binary heap in a static variable
static mut HEAP: BinaryHeap<i32, Max, 8> = BinaryHeap::new();

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impl<T, K, const N: usize> BinaryHeap<T, K, N>
where T: Ord, K: Kind,

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pub fn capacity(&self) -> usize

Returns the capacity of the binary heap.

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pub fn clear(&mut self)

Drops all items from the binary heap.

use heapless::binary_heap::{BinaryHeap, Max};

let mut heap: BinaryHeap<_, Max, 8> = BinaryHeap::new();
heap.push(1).unwrap();
heap.push(3).unwrap();

assert!(!heap.is_empty());

heap.clear();

assert!(heap.is_empty());

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pub fn len(&self) -> usize

Returns the length of the binary heap.

use heapless::binary_heap::{BinaryHeap, Max};

let mut heap: BinaryHeap<_, Max, 8> = BinaryHeap::new();
heap.push(1).unwrap();
heap.push(3).unwrap();

assert_eq!(heap.len(), 2);

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pub fn is_empty(&self) -> bool

Checks if the binary heap is empty.

use heapless::binary_heap::{BinaryHeap, Max};

let mut heap: BinaryHeap<_, Max, 8> = BinaryHeap::new();

assert!(heap.is_empty());

heap.push(3).unwrap();
heap.push(5).unwrap();
heap.push(1).unwrap();

assert!(!heap.is_empty());

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pub fn iter(&self) -> Iter<'_, T>

Returns an iterator visiting all values in the underlying vector, in arbitrary order.

use heapless::binary_heap::{BinaryHeap, Max};

let mut heap: BinaryHeap<_, Max, 8> = BinaryHeap::new();
heap.push(1).unwrap();
heap.push(2).unwrap();
heap.push(3).unwrap();
heap.push(4).unwrap();

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

}

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pub fn iter_mut(&mut self) -> IterMut<'_, T>

Returns a mutable iterator visiting all values in the underlying vector, in arbitrary order.

WARNING Mutating the items in the binary heap can leave the heap in an inconsistent state.

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

Returns the top (greatest if max-heap, smallest if min-heap) item in the binary heap, or None if it is empty.

use heapless::binary_heap::{BinaryHeap, Max};

let mut heap: BinaryHeap<_, Max, 8> = BinaryHeap::new();
assert_eq!(heap.peek(), None);

heap.push(1).unwrap();
heap.push(5).unwrap();
heap.push(2).unwrap();
assert_eq!(heap.peek(), Some(&5));

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pub fn peek_mut(&mut self) -> Option<PeekMut<'_, T, K, N>>

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 heapless::binary_heap::{BinaryHeap, Max};

let mut heap: BinaryHeap<_, Max, 8> = 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));

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

Removes the top (greatest if max-heap, smallest if min-heap) item from the binary heap and returns it, or None if it is empty.

use heapless::binary_heap::{BinaryHeap, Max};

let mut heap: BinaryHeap<_, Max, 8> = BinaryHeap::new();
heap.push(1).unwrap();
heap.push(3).unwrap();

assert_eq!(heap.pop(), Some(3));
assert_eq!(heap.pop(), Some(1));
assert_eq!(heap.pop(), None);

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pub unsafe fn pop_unchecked(&mut self) -> T

Removes the top (greatest if max-heap, smallest if min-heap) item from the binary heap and returns it, without checking if the binary heap is empty.

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pub fn push(&mut self, item: T) -> Result<(), T>

Pushes an item onto the binary heap.

use heapless::binary_heap::{BinaryHeap, Max};

let mut heap: BinaryHeap<_, Max, 8> = BinaryHeap::new();
heap.push(3).unwrap();
heap.push(5).unwrap();
heap.push(1).unwrap();

assert_eq!(heap.len(), 3);
assert_eq!(heap.peek(), Some(&5));