use core::mem::swap;
#[cfg(feature = "serde")]
use serde::{Deserialize, Serialize};
use self::heap_helpers::StaticHeapHole;
pub use self::heap_helpers::StaticHeapPeekMut;
pub use self::heap_iterators::{StaticHeapDrainSorted, StaticHeapIntoIterSorted};
use crate::iterators::{StaticVecDrain, StaticVecIterConst, StaticVecIterMut};
use crate::StaticVec;
mod heap_helpers;
mod heap_iterators;
mod heap_trait_impls;
/// A priority queue implemented as a binary heap, built around an instance of `StaticVec<T, N>`.
///
/// `StaticHeap`, as well as the associated iterator and helper structs for it are direct
/// adaptations of the ones found in the `std::collections::binary_heap` module (including
/// most of the documentation, at least for the functions that exist in both implementations).
///
/// 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 staticvec::StaticHeap;
///
/// let mut heap = StaticHeap::<i32, 4>::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())
/// ```
///
/// ## Min-heap
///
/// Either `core::cmp::Reverse` or a custom `Ord` implementation can be used to
/// make `StaticHeap` a min-heap. This makes `heap.pop()` return the smallest
/// value instead of the greatest one.
///
/// ```
/// use staticvec::StaticHeap;
/// use core::cmp::Reverse;
///
/// // Wrap the values in `Reverse`.
/// let mut heap = StaticHeap::from([Reverse(1), Reverse(5), 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);
/// ```
///
/// # 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.
///
/// [push]: #method.push
/// [pop]: #method.pop
/// [peek]: #method.peek
/// [peek\_mut]: #method.peek_mut
#[cfg_attr(feature = "serde", derive(Deserialize, Serialize))]
pub struct StaticHeap<T, const N: usize> {
pub(crate) data: StaticVec<T, N>,
}
impl<T: Ord, const N: usize> StaticHeap<T, N> {
/// Creates an empty StaticHeap as a max-heap.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::StaticHeap;
/// let mut heap = StaticHeap::<i32, 2>::new();
/// heap.push(4);
/// ```
#[inline(always)]
pub const fn new() -> StaticHeap<T, N> {
StaticHeap {
data: StaticVec::new(),
}
}
/// Returns a mutable reference to the greatest item in the StaticHeap, or
/// `None` if it is empty.
///
/// Note: If the `StaticHeapPeekMut` value is leaked, the heap may be in an
/// inconsistent state.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::StaticHeap;
/// let mut heap = StaticHeap::<i32, 4>::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
///
/// Cost is O(1) in the worst case.
#[inline(always)]
pub const fn peek_mut(&mut self) -> Option<StaticHeapPeekMut<'_, T, N>> {
if self.is_empty() {
None
} else {
Some(StaticHeapPeekMut {
heap: self,
sift: true,
})
}
}
/// Pops a value from the end of the StaticHeap and returns it directly without asserting that
/// the StaticHeap's current length is greater than 0.
///
/// # Safety
///
/// It is up to the caller to ensure that the StaticHeap contains at least one
/// element prior to using this function. Failure to do so will result in reading
/// from uninitialized memory.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let mut heap = StaticHeap::from([1, 3]);
/// unsafe {
/// assert_eq!(heap.pop_unchecked(), 3);
/// assert_eq!(heap.pop_unchecked(), 1);
/// }
/// ```
///
/// # Time complexity
///
/// The worst case cost of `pop_unchecked` on a heap containing *n* elements is O(log n).
#[inline(always)]
pub unsafe fn pop_unchecked(&mut self) -> T {
let mut res = self.data.pop_unchecked();
if self.is_not_empty() {
swap(&mut res, self.data.get_unchecked_mut(0));
self.sift_down_to_bottom(0);
}
res
}
/// Removes the greatest item from the StaticHeap and returns it, or `None` if it
/// is empty.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let mut heap = StaticHeap::from([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).
#[inline(always)]
pub fn pop(&mut self) -> Option<T> {
if self.is_empty() {
None
} else {
Some(unsafe { self.pop_unchecked() })
}
}
/// Pushes a value onto the StaticHeap without asserting that
/// its current length is less than `self.capacity()`.
///
/// # Safety
///
/// It is up to the caller to ensure that the length of the StaticHeap
/// prior to using this function is less than `self.capacity()`.
/// Failure to do so will result in writing to an out-of-bounds memory region.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::StaticHeap;
/// let mut heap = StaticHeap::<i32, 3>::new();
/// unsafe {
/// heap.push_unchecked(3);
/// heap.push_unchecked(5);
/// heap.push_unchecked(1);
/// }
/// assert_eq!(heap.len(), 3);
/// assert_eq!(heap.peek(), Some(&5));
/// ```
///
/// # Time complexity
///
/// The expected cost of `push_unchecked`, 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_unchecked` is O(n).
#[inline(always)]
pub unsafe fn push_unchecked(&mut self, item: T) {
let old_length = self.len();
self.data.push_unchecked(item);
self.sift_up(0, old_length);
}
/// Pushes an item onto the StaticHeap, panicking if the underlying StaticVec
/// instance is already at maximum capacity.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::StaticHeap;
/// let mut heap = StaticHeap::<i32, 5>::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).
#[inline(always)]
pub fn push(&mut self, item: T) {
// Deferring to our own `push_unchecked` which defers to `StaticVec::push_unchecked`
// is slower here than just calling `StaticVec::push` which calls `StaticVec::push_unchecked`
// anyways.
let old_length = self.len();
self.data.push(item);
self.sift_up(0, old_length);
}
/// Consumes the StaticHeap and returns a StaticVec in sorted (ascending) order.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let mut heap = StaticHeap::<i32, 8>::from([1, 2, 4, 5, 7]);
/// heap.push(6);
/// heap.push(3);
/// let vec = heap.into_sorted_staticvec();
/// assert_eq!(vec, [1, 2, 3, 4, 5, 6, 7]);
/// ```
#[inline]
pub fn into_sorted_staticvec(mut self) -> StaticVec<T, N> {
let mut end = self.len();
while end > 1 {
end -= 1;
self.data.swap(0, end);
self.sift_down_range(0, end);
}
self.into_staticvec()
}
// The implementations of sift_up and sift_down use unsafe blocks in
// order to move an element out of the vector (leaving behind a
// hole), shift along the others and move the removed element back into the
// vector at the final location of the hole.
// The `StaticHeapHole` type is used to represent this, and make sure
// the hole is filled back at the end of its scope, even on panic.
// Using a hole reduces the constant factor compared to using swaps,
// which involves twice as many moves.
#[inline]
fn sift_up(&mut self, start: usize, position: usize) {
unsafe {
// Take out the value at `position` and create a hole.
let mut hole = StaticHeapHole::new(&mut self.data, position);
while hole.pos() > start {
let parent = (hole.pos() - 1) / 2;
if hole.elt() <= hole.get(parent) {
break;
}
hole.move_to(parent);
}
}
}
/// Takes an element from `position` and moves it down the heap,
/// while its children are larger.
#[inline]
fn sift_down_range(&mut self, position: usize, end: usize) {
unsafe {
let mut hole = StaticHeapHole::new(&mut self.data, position);
let mut child = 2 * position + 1;
while child < end {
let right = child + 1;
// compare with the greater of the two children
if right < end && hole.get(child) <= hole.get(right) {
child = right;
}
// if we are already in order, stop.
if hole.elt() >= hole.get(child) {
break;
}
hole.move_to(child);
child = 2 * hole.pos() + 1;
}
}
}
/// Takes an element from `position` and moves it all the way down the heap,
/// then sifts it up to its position.
///
/// Note: This is faster when the element is known to be large / should
/// be closer to the bottom.
#[inline]
fn sift_down_to_bottom(&mut self, mut position: usize) {
let end = self.len();
let start = position;
unsafe {
let mut hole = StaticHeapHole::new(&mut self.data, position);
let mut child = 2 * position + 1;
while child < end {
let right = child + 1;
// compare with the greater of the two children
if right < end && hole.get(child) <= hole.get(right) {
child = right;
}
hole.move_to(child);
child = 2 * hole.pos() + 1;
}
position = hole.position;
}
self.sift_up(start, position);
}
#[inline(always)]
fn rebuild(&mut self) {
let mut n = self.len() / 2;
while n > 0 {
n -= 1;
self.sift_down_range(n, self.len());
}
}
/// Appends `self.remaining_capacity()` (or as many as available) items from `other` to `self`.
/// The appended items (if any) will no longer exist in `other` afterwards (which is to say,
/// `other` will be left empty.)
///
/// The `N2` parameter does not need to be provided explicitly, and can be inferred directly from
/// the constant `N2` constraint of `other` (which may or may not be the same as the `N`
/// constraint of `self`.)
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// // We give the two heaps arbitrary capacities for the sake of the example.
/// let mut a = StaticHeap::<i32, 9>::from([-10, 1, 2, 3, 3]);
/// let mut b = StaticHeap::<i32, 18>::from([-20, 5, 43]);
/// a.append(&mut b);
/// assert_eq!(a.into_sorted_staticvec(), [-20, -10, 1, 2, 3, 3, 5, 43]);
/// assert!(b.is_empty());
/// ```
#[inline(always)]
pub fn append<const N2: usize>(&mut self, other: &mut StaticHeap<T, N2>) {
if other.is_empty() {
return;
}
self.data.append(&mut other.data);
self.rebuild();
}
/// 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:
/// ```
/// # use staticvec::*;
/// let mut heap = StaticHeap::from([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);
/// ```
#[inline(always)]
pub const fn drain_sorted(&mut self) -> StaticHeapDrainSorted<'_, T, N> {
StaticHeapDrainSorted { inner: self }
}
}
impl<T, const N: usize> StaticHeap<T, N> {
/// Returns an iterator visiting all values in the StaticHeap's underlying StaticVec, in
/// arbitrary order.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let heap = StaticHeap::from(staticvec![1, 2, 3, 4]);
/// // Print 1, 2, 3, 4 in arbitrary order
/// for x in heap.iter() {
/// println!("{}", x);
/// }
/// ```
#[inline(always)]
pub const fn iter(&self) -> StaticVecIterConst<'_, T, N> {
self.data.iter()
}
/// Returns a mutable iterator visiting all values in the StaticHeap's underlying StaticVec, in
/// arbitrary order.
///
/// **Note:** Mutating the elements in a StaticHeap may cause it to become unbalanced.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let mut heap = StaticHeap::from([1, 2, 3, 4]);
/// for i in heap.iter_mut() {
/// *i *= 2;
/// }
/// // Prints "[2, 4, 6, 8]", but in arbitrary order
/// println!("{:?}", heap);
/// ```
#[inline(always)]
pub const fn iter_mut(&mut self) -> StaticVecIterMut<'_, T, N> {
self.data.iter_mut()
}
/// Returns an iterator which retrieves elements in heap order.
/// This method consumes the original StaticHeap.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let heap = StaticHeap::from([1, 2, 3, 4, 5]);
/// assert_eq!(
/// heap.into_iter_sorted().take(2).collect::<StaticVec<_, 3>>(), staticvec![5, 4]
/// );
/// ```
#[inline(always)]
pub const fn into_iter_sorted(self) -> StaticHeapIntoIterSorted<T, N> {
StaticHeapIntoIterSorted { inner: self }
}
/// Returns the greatest item in the StaticHeap, or `None` if it is empty.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let mut heap = StaticHeap::<i32, 7>::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.
#[inline(always)]
pub fn peek(&self) -> Option<&T> {
self.data.get(0)
}
/// Returns the maximum number of elements the StaticHeap can hold.
/// This is always equivalent to its constant generic `N` parameter.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let mut heap = StaticHeap::<i32, 100>::new();
/// assert!(heap.capacity() >= 100);
/// heap.push(4);
/// ```
#[inline(always)]
pub const fn capacity(&self) -> usize {
self.data.capacity()
}
/// Returns the remaining capacity (which is to say, `self.capacity() - self.len()`) of the
/// StaticHeap.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let mut heap = StaticHeap::<i32, 100>::new();
/// heap.push(1);
/// assert_eq!(heap.remaining_capacity(), 99);
/// ```
#[inline(always)]
pub const fn remaining_capacity(&self) -> usize {
self.data.remaining_capacity()
}
/// Returns the total size of the inhabited part of the StaticHeap (which may be zero if it has a
/// length of zero or contains ZSTs) in bytes. Specifically, the return value of this function
/// amounts to a calculation of `size_of::<T>() * self.length`.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let x = StaticHeap::<u8, 8>::from([1, 2, 3, 4, 5, 6, 7, 8]);
/// assert_eq!(x.size_in_bytes(), 8);
/// let y = StaticHeap::<u16, 8>::from([1, 2, 3, 4, 5, 6, 7, 8]);
/// assert_eq!(y.size_in_bytes(), 16);
/// let z = StaticHeap::<u32, 8>::from([1, 2, 3, 4, 5, 6, 7, 8]);
/// assert_eq!(z.size_in_bytes(), 32);
/// let w = StaticHeap::<u64, 8>::from([1, 2, 3, 4, 5, 6, 7, 8]);
/// assert_eq!(w.size_in_bytes(), 64);
/// ```
#[inline(always)]
pub const fn size_in_bytes(&self) -> usize {
self.data.size_in_bytes()
}
/// Consumes the StaticHeap and returns the underlying StaticVec
/// in arbitrary order.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let heap = StaticHeap::from(staticvec![1, 2, 3, 4, 5, 6, 7]);
/// let vec = heap.into_staticvec();
/// // Will print in some order
/// for x in &vec {
/// println!("{}", x);
/// }
/// ```
#[inline(always)]
pub fn into_staticvec(self) -> StaticVec<T, N> {
self.data
}
/// Returns the length of the StaticHeap.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let heap = StaticHeap::from(staticvec![1, 3]);
/// assert_eq!(heap.len(), 2);
/// ```
#[inline(always)]
pub const fn len(&self) -> usize {
self.data.len()
}
/// Returns true if the current length of the StaticHeap is 0.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let mut heap = StaticHeap::<i32, 28>::new();
/// assert!(heap.is_empty());
/// ```
#[inline(always)]
pub const fn is_empty(&self) -> bool {
self.len() == 0
}
/// Returns true if the current length of the StaticHeap is greater than 0.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let mut heap = StaticHeap::<i32, 2>::new();
/// heap.push(1);
/// assert!(heap.is_not_empty());
/// ```
// Clippy wants `!is_empty()` for this, but I prefer it as-is. My question is though, does it
// actually know that we have an applicable `is_empty()` function, or is it just guessing? I'm not
// sure.
#[allow(clippy::len_zero)]
#[inline(always)]
pub const fn is_not_empty(&self) -> bool {
self.len() > 0
}
/// Returns true if the current length of the StaticHeap is equal to its capacity.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let mut heap = StaticHeap::<i32, 4>::new();
/// heap.push(3);
/// heap.push(5);
/// heap.push(1);
/// heap.push(2);
/// assert!(heap.is_full());
/// ```
#[inline(always)]
pub const fn is_full(&self) -> bool {
self.len() == N
}
/// Returns true if the current length of the StaticHeap is less than its capacity.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let mut heap = StaticHeap::<i32, 4>::new();
/// heap.push(3);
/// heap.push(5);
/// heap.push(1);
/// assert!(heap.is_not_full());
/// ```
#[inline(always)]
pub const fn is_not_full(&self) -> bool {
self.len() < N
}
/// Clears the StaticHeap, returning an iterator over the removed elements.
///
/// The elements are removed in arbitrary order.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let mut heap = StaticHeap::from(staticvec![1, 3]);
/// assert!(heap.is_not_empty());
/// for x in heap.drain() {
/// println!("{}", x);
/// }
/// assert!(heap.is_empty());
/// ```
#[inline(always)]
pub fn drain(&mut self) -> StaticVecDrain<'_, T, N> {
self.data.drain_iter(..)
}
/// Drops all items from the StaticHeap.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use staticvec::*;
/// let mut heap = StaticHeap::from(staticvec![1, 3]);
/// assert!(heap.is_not_empty());
/// heap.clear();
/// assert!(heap.is_empty());
/// ```
#[inline(always)]
pub fn clear(&mut self) {
self.data.clear();
}
}