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Auto merge of #93765 - zhangyunhao116:heapsort, r=m-ou-se

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Optimize heapsort

The new implementation is about 10% faster than the previous one(sorting random 1000 items).
This commit is contained in:
bors 2022-06-20 18:09:30 +00:00
commit 5750a6aa27
1 changed files with 11 additions and 8 deletions
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19
library/core/src/slice/sort.rs
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@ -188,22 +188,25 @@ pub fn heapsort<T, F>(v: &mut [T], mut is_less: F)
// This binary heap respects the invariant `parent >= child`.
let mut sift_down = |v: &mut [T], mut node| {
loop {
// Children of `node`:
let left = 2 * node + 1;
let right = 2 * node + 2;
// Children of `node`.
let mut child = 2 * node + 1;
if child >= v.len() {
break;
}
// Choose the greater child.
let greater =
if right < v.len() && is_less(&v[left], &v[right]) { right } else { left };
if child + 1 < v.len() && is_less(&v[child], &v[child + 1]) {
child += 1;
}
// Stop if the invariant holds at `node`.
if greater >= v.len() || !is_less(&v[node], &v[greater]) {
if !is_less(&v[node], &v[child]) {
break;
}
// Swap `node` with the greater child, move one step down, and continue sifting.
v.swap(node, greater);
node = greater;
v.swap(node, child);
node = child;
}
};