Struct WeakHeap

pub struct WeakHeap<T> { /* private fields */ }

A priority queue implemented with a weak heap.

This will be a max-heap.

Examples

use weakheap::WeakHeap;

// Type inference lets us omit an explicit type signature (which
// would be `WeakHeap<i32>` in this example).
let mut heap = WeakHeap::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.iter() {
    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 WeakHeap with a known list of items can be initialized from an array:

use weakheap::WeakHeap;

let heap = WeakHeap::from([1, 5, 2]);

Min-heap

Either core::cmp::Reverse or a custom Ord implementation can be used to make WeakHeap a min-heap. This makes heap.pop() return the smallest value instead of the greatest one.

use weakheap::WeakHeap;
use std::cmp::Reverse;

let mut heap = WeakHeap::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);

Sorting

use weakheap::WeakHeap;

let heap = WeakHeap::from([5, 3, 1, 7]);
assert_eq!(heap.into_sorted_vec(), vec![1, 3, 5, 7]);

Time complexity

push	pop	peek/peek_mut	into_sorted_vec
O(1)~	O(log(n))	O(1)	O(nlog(n))

The value for push is an expected cost; the method documentation gives a more detailed analysis.

Implementations

impl<T: Ord> WeakHeap<T>

pub fn new() -> WeakHeap<T>

Creates an empty WeakHeap as a max-heap.

Examples

Basic usage:

use weakheap::WeakHeap;
let mut heap = WeakHeap::new();
assert!(heap.is_empty());

heap.push(4);
assert_eq!(heap.len(), 1);

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

Creates an empty WeakHeap with a specific capacity. This preallocates enough memory for capacity elements, so that the WeakHeap does not have to be reallocated until it contains at least that many values.

Examples

Basic usage:

use weakheap::WeakHeap;
let mut heap = WeakHeap::with_capacity(10);
heap.push(4);

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

Returns a mutable reference to the greatest item in the weak heap, or None if it is empty.

Note: If the WeakHeapPeekMut value is leaked, the heap may be in an inconsistent state.

Examples

Basic usage:

use weakheap::WeakHeap;
let mut heap = WeakHeap::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

If the item is modified then the worst case time complexity is O(log(n)), otherwise it’s O(1).

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

Removes the greatest item from the weak heap and returns it, or None if it is empty.

Examples

Basic usage:

use weakheap::WeakHeap;
let mut heap = WeakHeap::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)).

Sifting down in a weak heap can be done in log(2, n) comparisons, as opposed to 2log(2, n) for binary heap.

pub fn push(&mut self, item: T)

Pushes an item onto the binary heap.

Examples

Basic usage:

use weakheap::WeakHeap;
let mut heap = WeakHeap::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 pushpop(&mut self, item: T) -> T

Effective equivalent to a sequential push() and pop() calls.

Examples

Basic usage:

use weakheap::WeakHeap;
let mut heap = WeakHeap::new();
assert_eq!(heap.pushpop(5), 5);
assert!(heap.is_empty());

heap.push(10);
assert_eq!(heap.pushpop(20), 20);
assert_eq!(heap.peek(), Some(&10));

assert_eq!(heap.pushpop(5), 10);
assert_eq!(heap.peek(), Some(&5));

Time complexity

If the heap is empty or the element being added is larger (or equal) than the current top of the heap, then the time complexity will be O(1), otherwise O(log(n)). And unlike the sequential call of push() and pop(), the resizing never happens.

pub fn into_sorted_vec(self) -> Vec<T>

Consumes the WeakHeap and returns a vector in sorted (ascending) order.

Examples

Basic usage:

use weakheap::WeakHeap;

let mut heap = WeakHeap::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]);

Time complexity

Operation can be done in O(nlog(n)) like conventional heapsort, but sorting by a weak heap produces significantly fewer comparisons.

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

Moves all the elements of other into self, leaving other empty.

Examples

Basic usage:

use weakheap::WeakHeap;

let v = vec![-10, 1, 2, 3, 3];
let mut a = WeakHeap::from(v);

let v = vec![-20, 5, 43];
let mut b = WeakHeap::from(v);

a.append(&mut b);

assert_eq!(a.into_sorted_vec(), [-20, -10, 1, 2, 3, 3, 5, 43]);
assert!(b.is_empty());

Time complexity

Operation can be done in O(nlog(n)) in worst case, but average time complexity is O(n), where n = self.len() + other.len().

pub fn append_vec(&mut self, other: &mut Vec<T>)

Moves all the elements of vector other into self, leaving other empty.

Examples

Basic usage:

use weakheap::WeakHeap;

let mut a = WeakHeap::from(vec![-10, 1, 2, 3, 3]);

let mut v = vec![-20, 5, 43];
a.append_vec(&mut v);

assert_eq!(a.into_sorted_vec(), [-20, -10, 1, 2, 3, 3, 5, 43]);
assert!(v.is_empty());

Time complexity

Operation can be done in O(nlog(n)) in worst case, but average time complexity is O(n), where n = self.len() + other.len().

impl<T> WeakHeap<T>

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

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

Examples

Basic usage:

use weakheap::WeakHeap;
let heap = WeakHeap::from(vec![1, 2, 3, 4]);

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

assert_eq!(heap.into_sorted_vec(), vec![1, 2, 3, 4]);

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

Returns the greatest item in the weak heap, or None if it is empty.

Examples

Basic usage:

use weakheap::WeakHeap;
let mut heap = WeakHeap::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 weak heap can hold without reallocating.

Examples

Basic usage:

use weakheap::WeakHeap;
let mut heap = WeakHeap::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 WeakHeap. 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 weakheap::WeakHeap;
let mut heap = WeakHeap::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 WeakHeap. The collection may reserve more space to avoid frequent reallocations.

Panics

Panics if the new capacity overflows usize.

Examples

Basic usage:

use weakheap::WeakHeap;
let mut heap = WeakHeap::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 weakheap::WeakHeap;
let mut heap: WeakHeap<i32> = WeakHeap::with_capacity(100);

assert!(heap.capacity() >= 100);
heap.shrink_to_fit();
assert!(heap.capacity() == 0);

pub fn shrink_to(&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 weakheap::WeakHeap;
let mut heap: WeakHeap<i32> = WeakHeap::with_capacity(100);

assert!(heap.capacity() >= 100);
heap.shrink_to(10);
assert!(heap.capacity() >= 10);

pub fn into_vec(self) -> Vec<T>

Consumes the WeakHeap<T> and returns the underlying vector Vec in arbitrary order.

The results of WeakHeap::into_vec() and BinaryHeap::into_vec() are likely to differ.

Examples

Basic usage:

use weakheap::WeakHeap;
let heap = WeakHeap::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 weak heap.

Examples

Basic usage:

use weakheap::WeakHeap;
let heap = WeakHeap::from(vec![1, 3]);

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

pub fn is_empty(&self) -> bool

Checks if the weak heap is empty.

Examples

Basic usage:

use weakheap::WeakHeap;
let mut heap = WeakHeap::new();

assert!(heap.is_empty());

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

assert!(!heap.is_empty());

pub fn drain(&mut self) -> Drain<'_, T>

Clears the weak heap, returning an iterator over the removed elements.

The elements are removed in arbitrary order.

Examples

Basic usage:

use weakheap::WeakHeap;
let mut heap = WeakHeap::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 weak heap.

Examples

Basic usage:

use weakheap::WeakHeap;
let mut heap = WeakHeap::from(vec![1, 3]);

assert!(!heap.is_empty());

heap.clear();

assert!(heap.is_empty());

Trait Implementations

impl<T: Clone> Clone for WeakHeap<T>

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T: Debug> Debug for WeakHeap<T>

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

Formats the value using the given formatter.

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

fn default() -> WeakHeap<T>

Creates an empty WeakHeap as a max-heap.

Examples

Basic usage:

use weakheap::WeakHeap;
let mut heap = WeakHeap::default();
assert!(heap.is_empty());

heap.push(4);
assert_eq!(heap.len(), 1);

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

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

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (extend_one)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (extend_one)

Reserves capacity in a collection for the given number of additional elements.

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

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

Extend WeakHeap with elements from the iterator.

Examples

Basic usage:

use weakheap::WeakHeap;

let mut heap = WeakHeap::new();
heap.extend(vec![7, 1, 0, 4, 5, 3]);
assert_eq!(heap.into_sorted_vec(), [0, 1, 3, 4, 5, 7]);

fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (extend_one)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (extend_one)

Reserves capacity in a collection for the given number of additional elements.

impl<T: Ord, const N: usize> From<[T; N]> for WeakHeap<T>

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

Converts a [T, N] into a WeakHeap<T>.

This conversion has O(n) time complexity.

Examples

Basic usage:

use weakheap::WeakHeap;

let mut h1 = WeakHeap::from([1, 4, 2, 3]);
let mut h2: WeakHeap<_> = [1, 4, 2, 3].into();
while let Some((a, b)) = h1.pop().zip(h2.pop()) {
    assert_eq!(a, b);
}

impl<T: Ord> From<Vec<T>> for WeakHeap<T>

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

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

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

Examples

Basic usage:

use weakheap::WeakHeap;
let heap = WeakHeap::from(vec![5, 3, 2, 4, 1]);
assert_eq!(heap.into_sorted_vec(), vec![1, 2, 3, 4, 5]);

impl<T> From<WeakHeap<T>> for Vec<T>

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

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

This conversion requires no data movement or allocation, and has constant time complexity.

Examples

Basic usage:

use weakheap::WeakHeap;

let mut heap = WeakHeap::from([1, 3, 2]);
let vec: Vec<i32> = heap.into();
assert_eq!(vec, vec![3, 2, 1]);

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

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

Building WeakHeap from iterator.

This conversion has O(n) time complexity.

Examples

Basic usage:

use weakheap::WeakHeap;

let mut h1 = WeakHeap::from([1, 4, 2, 3]);
let mut h2: WeakHeap<i32> = [1, 4, 2, 3].into_iter().collect();
while let Some((a, b)) = h1.pop().zip(h2.pop()) {
    assert_eq!(a, b);
}

impl<'a, T> IntoIterator for &'a WeakHeap<T>

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

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

Examples

Basic usage:

use weakheap::WeakHeap;
let heap = WeakHeap::from(vec![1, 2, 3, 4]);

// Print 1, 2, 3, 4 in arbitrary order
for x in &heap {
    // x has type &i32
    println!("{}", x);
}

assert_eq!(heap.into_sorted_vec(), vec![1, 2, 3, 4]);

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?

impl<T> IntoIterator for WeakHeap<T>

fn into_iter(self) -> IntoIter<T>

Creates a consuming iterator, that is, one that moves each value out of the weak heap in arbitrary order. The weak heap cannot be used after calling this.

Examples

Basic usage:

use weakheap::WeakHeap;
let heap = WeakHeap::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);
}

type Item = T

The type of the elements being iterated over.

type IntoIter = IntoIter<T>

Which kind of iterator are we turning this into?