Struct MinHeap

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

A min priority queue implemented as a thin wrapper around BinaryHeap<Reverse<T>>.

Examples

use min_heap::MinHeap;

// Type inference lets us omit an explicit type signature (which
// would be `MinHeap<i32>` in this example).
let mut heap = MinHeap::new();

// We can use peek to look at the smallest 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 smallest item in the heap.
assert_eq!(heap.peek(), Some(&1));

// 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
// an unspecified order.
for x in &heap {
    println!("{x}");
}

// If we instead pop these scores, they should come back in order.
assert_eq!(heap.pop(), Some(1));
assert_eq!(heap.pop(), Some(2));
assert_eq!(heap.pop(), Some(5));
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 MinHeap with a known list of items can be initialized from an array:

use min_heap::MinHeap;

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

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> MinHeap<T>

where T: Ord,

pub const fn new() -> Self

Creates an empty min-heap.

Examples

Basic usage:

use min_heap::MinHeap;
let mut heap = MinHeap::new();
heap.push(4);

pub fn with_capacity(capacity: usize) -> Self

Creates an empty MinHeap with at least the specified capacity.

The 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 heap will not allocate.

Examples

Basic usage:

use min_heap::MinHeap;
let mut heap = MinHeap::with_capacity(10);
heap.push(4);

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

Returns a mutable reference to the smallest item in the 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 min_heap::MinHeap;
let mut heap = MinHeap::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 = 8;
}
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 smallest item from the heap and returns it, or None if it is empty.

Examples

Basic usage:

use min_heap::MinHeap;
let mut heap = MinHeap::from([1, 3]);

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

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)

Pushes an item onto the heap.

Examples

Basic usage:

use min_heap::MinHeap;
let mut heap = MinHeap::new();
heap.push(5);
heap.push(1);
heap.push(3);

assert_eq!(heap.len(), 3);
assert_eq!(heap.peek(), Some(&1));

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 decreasing order. In the worst case, elements are pushed in decreasing 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 into_sorted_vec(self) -> Vec<T>

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

Examples

Basic usage:

use min_heap::MinHeap;

let mut heap = MinHeap::from([5, 2, 4, 1, 7]);
heap.push(6);
heap.push(3);

let vec = heap.into_sorted_vec();
assert_eq!(vec, [1, 2, 3, 4, 5, 6, 7]);

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

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

Examples

Basic usage:

use min_heap::MinHeap;

let mut a = MinHeap::from([-10, 1, 2, 3, 3]);
let mut b = MinHeap::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());

pub fn retain<F>(&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 min_heap::MinHeap;

let mut heap = MinHeap::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<T> MinHeap<T>

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

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

Examples

Basic usage:

use min_heap::MinHeap;
let heap = MinHeap::from([1, 2, 3, 4]);

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

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

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

Examples

Basic usage:

use min_heap::MinHeap;
let mut heap = MinHeap::new();
assert_eq!(heap.peek(), None);

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

Time complexity

Cost is O(1) in the worst case.

pub fn capacity(&self) -> usize

Returns the number of elements the heap can hold without reallocating.

Examples

Basic usage:

use min_heap::MinHeap;
let mut heap = MinHeap::with_capacity(100);
assert!(heap.capacity() >= 100);
heap.push(4);

pub fn reserve_exact(&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 min_heap::MinHeap;
let mut heap = MinHeap::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 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 min_heap::MinHeap;
let mut heap = MinHeap::new();
heap.reserve(100);
assert!(heap.capacity() >= 100);
heap.push(4);

pub fn try_reserve_exact( &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 min_heap::MinHeap;
use std::collections::TryReserveError;

fn find_min_slow(data: &[u32]) -> Result<Option<u32>, TryReserveError> {
    let mut heap = MinHeap::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())
}

pub fn try_reserve(&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 min_heap::MinHeap;
use std::collections::TryReserveError;

fn find_min_slow(data: &[u32]) -> Result<Option<u32>, TryReserveError> {
    let mut heap = MinHeap::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())
}

pub fn shrink_to_fit(&mut self)

Discards as much additional capacity as possible.

Examples

Basic usage:

use min_heap::MinHeap;
let mut heap: MinHeap<i32> = MinHeap::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 min_heap::MinHeap;
let mut heap: MinHeap<i32> = MinHeap::with_capacity(100);

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

pub fn as_slice(&self) -> &[T]

Returns a slice of all values in the underlying vector, in arbitrary order.

Examples

Basic usage:

use min_heap::MinHeap;
use std::io::{self, Write};

let heap = MinHeap::from([1, 2, 3, 4, 5, 6, 7]);

io::sink().write(heap.as_slice()).unwrap();

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

Consumes the MinHeap and returns the underlying vector in arbitrary order.

Examples

Basic usage:

use min_heap::MinHeap;
let heap = MinHeap::from([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 heap.

Examples

Basic usage:

use min_heap::MinHeap;
let heap = MinHeap::from([1, 3]);

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

pub fn is_empty(&self) -> bool

Checks if the heap is empty.

Examples

Basic usage:

use min_heap::MinHeap;
let mut heap = MinHeap::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 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 min_heap::MinHeap;
let mut heap = MinHeap::from([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 heap.

Examples

Basic usage:

use min_heap::MinHeap;
let mut heap = MinHeap::from([1, 3]);

assert!(!heap.is_empty());

heap.clear();

assert!(heap.is_empty());

Trait Implementations

impl<T: Clone> Clone for MinHeap<T>

fn clone(&self) -> MinHeap<T>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T: Debug> Debug for MinHeap<T>

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

Formats the value using the given formatter.

impl<T> Default for MinHeap<T>

where T: Ord,

fn default() -> Self

Returns the “default value” for a type.

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

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

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, const N: usize> From<[T; N]> for MinHeap<T>

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

use min_heap::MinHeap;

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

impl<T> From<MinHeap<T>> for Vec<T>

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

Converts a MinHeap<T> into a Vec<T>. The order of the elements in the resulting Vec<T> is unspecified (most likely unsorted).

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

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

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

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

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

Example

use min_heap::MinHeap;

let v = vec![3, 12, 5, 6, 9];
let mut h: MinHeap<_> = v.into();
assert_eq!(h.pop(), Some(3));
assert_eq!(h.pop(), Some(5));
assert_eq!(h.pop(), Some(6));
assert_eq!(h.pop(), Some(9));
assert_eq!(h.pop(), Some(12));
assert_eq!(h.pop(), None);

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

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

Creates a value from an iterator.

impl<T> Hash for MinHeap<T>

where BinaryHeap<Reverse<T>>: Hash,

fn hash<H: Hasher>(&self, state: &mut H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

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

type Item = &'a T

The type of the elements being iterated over.

type IntoIter = IterRefWrapper<'a, Iter<'a, Reverse<T>>, T>

Which kind of iterator are we turning this into?

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

Creates an iterator from a value.

impl<T> IntoIterator for MinHeap<T>

fn into_iter(self) -> IntoIter<T>

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

Examples

Basic usage:

use min_heap::MinHeap;
let heap = MinHeap::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}");
}

type Item = T

The type of the elements being iterated over.

type IntoIter = IterWrapper<IntoIter<Reverse<T>>, T>

Which kind of iterator are we turning this into?

impl<T> Ord for MinHeap<T>

where BinaryHeap<Reverse<T>>: Ord,

fn cmp(&self, other: &Self) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl<T> PartialEq for MinHeap<T>

where BinaryHeap<Reverse<T>>: PartialEq,

fn eq(&self, other: &Self) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T> PartialOrd for MinHeap<T>

where BinaryHeap<Reverse<T>>: PartialOrd,

fn partial_cmp(&self, other: &Self) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl<T> Eq for MinHeap<T>

where BinaryHeap<Reverse<T>>: Eq,