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// this lib migrate from official lib, but without std dependency;
use core::mem::{swap, ManuallyDrop};
use core::ptr;
pub struct BinaryHeap<T> {
data: Vec<T>,
}
impl<T: Ord> BinaryHeap<T> {
pub fn new() -> BinaryHeap<T> {
BinaryHeap { data: vec![] }
}
pub fn with_capacity(capacity: usize) -> BinaryHeap<T> {
BinaryHeap {
data: Vec::with_capacity(capacity),
}
}
pub fn pop(&mut self) -> Option<T> {
self.data.pop().map(|mut item| {
if !self.is_empty() {
swap(&mut item, &mut self.data[0]);
self.sift_down_to_bottom(0);
}
item
})
}
pub fn push(&mut self, item: T) {
let old_len = self.len();
self.data.push(item);
self.sift_up(0, old_len);
}
pub fn into_sorted_vec(mut self) -> Vec<T> {
let mut end = self.len();
while end > 1 {
end -= 1;
// SAFETY: `end` goes from `self.len() - 1` to 1 (both included),
// so it's always a valid index to access.
// It is safe to access index 0 (i.e. `ptr`), because
// 1 <= end < self.len(), which means self.len() >= 2.
unsafe {
let ptr = self.data.as_mut_ptr();
ptr::swap(ptr, ptr.add(end));
}
self.sift_down_range(0, end);
}
self.into_vec()
}
fn sift_up(&mut self, start: usize, pos: usize) -> usize {
unsafe {
// Take out the value at `pos` and create a hole.
let mut hole = Hole::new(&mut self.data, pos);
while hole.pos() > start {
let parent = (hole.pos() - 1) / 2;
if hole.element() <= hole.get(parent) {
break;
}
hole.move_to(parent);
}
hole.pos()
}
}
fn sift_down_range(&mut self, pos: usize, end: usize) {
unsafe {
let mut hole = Hole::new(&mut self.data, pos);
let mut child = 2 * pos + 1;
while child < end - 1 {
// compare with the greater of the two children
child += (hole.get(child) <= hole.get(child + 1)) as usize;
// if we are already in order, stop.
if hole.element() >= hole.get(child) {
return;
}
hole.move_to(child);
child = 2 * hole.pos() + 1;
}
if child == end - 1 && hole.element() < hole.get(child) {
hole.move_to(child);
}
}
}
fn sift_down(&mut self, pos: usize) {
let len = self.len();
self.sift_down_range(pos, len);
}
fn sift_down_to_bottom(&mut self, mut pos: usize) {
let end = self.len();
let start = pos;
unsafe {
let mut hole = Hole::new(&mut self.data, pos);
let mut child = 2 * pos + 1;
while child < end - 1 {
child += (hole.get(child) <= hole.get(child + 1)) as usize;
hole.move_to(child);
child = 2 * hole.pos() + 1;
}
if child == end - 1 {
hole.move_to(child);
}
pos = hole.pos;
}
self.sift_up(start, pos);
}
fn rebuild(&mut self) {
let mut n = self.len() / 2;
while n > 0 {
n -= 1;
self.sift_down(n);
}
}
pub fn retain<F>(&mut self, f: F)
where
F: FnMut(&T) -> bool,
{
self.data.retain(f);
self.rebuild();
}
}
impl<T> BinaryHeap<T> {
// pub fn iter(&self) -> Iter<'_, T> {
// Iter { iter: self.data.iter() }
// }
pub fn peek(&self) -> Option<&T> {
self.data.get(0)
}
pub fn capacity(&self) -> usize {
self.data.capacity()
}
pub fn reserve_exact(&mut self, additional: usize) {
self.data.reserve_exact(additional);
}
pub fn reserve(&mut self, additional: usize) {
self.data.reserve(additional);
}
pub fn shrink_to_fit(&mut self) {
self.data.shrink_to_fit();
}
pub fn into_vec(self) -> Vec<T> {
self.into()
}
pub fn len(&self) -> usize {
self.data.len()
}
pub fn is_empty(&self) -> bool {
self.len() == 0
}
pub fn clear(&mut self) {
self.data.drain(..);
}
}
/// Hole represents a hole in a slice i.e., an index without valid value
/// (because it was moved from or duplicated).
/// In drop, `Hole` will restore the slice by filling the hole
/// position with the value that was originally removed.
struct Hole<'a, T: 'a> {
data: &'a mut [T],
elt: ManuallyDrop<T>,
pos: usize,
}
impl<'a, T> Hole<'a, T> {
/// Create a new `Hole` at index `pos`.
///
/// Unsafe because pos must be within the data slice.
#[inline]
unsafe fn new(data: &'a mut [T], pos: usize) -> Self {
debug_assert!(pos < data.len());
// SAFE: pos should be inside the slice
let elt = unsafe { ptr::read(data.get_unchecked(pos)) };
Hole {
data,
elt: ManuallyDrop::new(elt),
pos,
}
}
#[inline]
fn pos(&self) -> usize {
self.pos
}
/// Returns a reference to the element removed.
#[inline]
fn element(&self) -> &T {
&self.elt
}
/// Returns a reference to the element at `index`.
///
/// Unsafe because index must be within the data slice and not equal to pos.
#[inline]
unsafe fn get(&self, index: usize) -> &T {
debug_assert!(index != self.pos);
debug_assert!(index < self.data.len());
unsafe { self.data.get_unchecked(index) }
}
/// Move hole to new location
///
/// Unsafe because index must be within the data slice and not equal to pos.
#[inline]
unsafe fn move_to(&mut self, index: usize) {
debug_assert!(index != self.pos);
debug_assert!(index < self.data.len());
unsafe {
let ptr = self.data.as_mut_ptr();
let index_ptr: *const _ = ptr.add(index);
let hole_ptr = ptr.add(self.pos);
ptr::copy_nonoverlapping(index_ptr, hole_ptr, 1);
}
self.pos = index;
}
}
impl<T> Drop for Hole<'_, T> {
#[inline]
fn drop(&mut self) {
// fill the hole again
unsafe {
let pos = self.pos;
ptr::copy_nonoverlapping(&*self.elt, self.data.get_unchecked_mut(pos), 1);
}
}
}
impl<T: Ord> From<Vec<T>> for BinaryHeap<T> {
/// Converts a `Vec<T>` into a `BinaryHeap<T>`.
///
/// This conversion happens in-place, and has *O*(*n*) time complexity.
fn from(vec: Vec<T>) -> BinaryHeap<T> {
let mut heap = BinaryHeap { data: vec };
heap.rebuild();
heap
}
}
impl<T> From<BinaryHeap<T>> for Vec<T> {
/// Converts a `BinaryHeap<T>` into a `Vec<T>`.
///
/// This conversion requires no data movement or allocation, and has
/// constant time complexity.
fn from(heap: BinaryHeap<T>) -> Vec<T> {
heap.data
}
}