Anson/Go-v-Rust-Quicksort
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THE RUST ALGO

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Anson 2022-04-25 15:12:22 -07:00
parent 631752f28b
commit 0aa9c50fff
1 changed files with 27 additions and 24 deletions
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51
rust/src/main.rs
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@ -3,23 +3,19 @@
use rayon::join; use rayon::join;
fn choose_pivot<T: Ord>(slice: &[T]) -> usize { fn choose_pivot<T: Ord>(slice: &[T]) -> usize {
// if slice.len() <= 2 {return slice.len() - 1;}; let (mut left, mid, mut right) = (0, slice.len() / 2, slice.len() - 1);
let (mut ismall, imid, mut ibig) = (0, slice.len() / 2, slice.len() - 1); if slice[right] < slice[left] {
if slice[ibig] < slice[ismall] { std::mem::swap(&mut right, &mut left);
std::mem::swap(&mut ibig, &mut ismall);
} }
if slice[imid] <= slice[ismall] { if slice[mid] <= slice[left] {
ismall return left;
} else if slice[ibig] <= slice[imid] { } else if slice[right] <= slice[mid] {
ibig return right;
} else { } else {
imid return mid;
} }
} }
/// choose a pivot, then reorder so that everything to the left of the pivot is smaller, and
/// everything to the right is greater
/// Assumes slice.len() > 2
fn partition<T: Ord>(slice: &mut [T], pivot: usize) -> usize { fn partition<T: Ord>(slice: &mut [T], pivot: usize) -> usize {
let mxix = slice.len() - 1; let mxix = slice.len() - 1;
slice.swap(pivot, mxix); slice.swap(pivot, mxix);
@ -52,10 +48,7 @@ fn partition<T: Ord>(slice: &mut [T], pivot: usize) -> usize {
return left + 1; return left + 1;
} }
panic!( panic!("partition failed.")
"This should be unreachable. Indices: {}, {} / {}",
left, right, mxix
);
} }
fn quicksort<T: Ord + std::marker::Send>(slice: &mut [T]) { fn quicksort<T: Ord + std::marker::Send>(slice: &mut [T]) {
@ -68,11 +61,10 @@ fn quicksort<T: Ord + std::marker::Send>(slice: &mut [T]) {
return; return;
} }
let pivot = choose_pivot(slice); let pivot = partition(slice, choose_pivot(slice));
let pivot = partition(slice, pivot);
let (left_slice, right_slice) = slice.split_at_mut(pivot); let (left_slice, right_slice) = slice.split_at_mut(pivot);
let right_slice = &mut right_slice[1..]; let right_slice = &mut right_slice[1..]; // want to exclude pivot
quicksort(left_slice); quicksort(left_slice);
quicksort(right_slice); quicksort(right_slice);
@ -88,12 +80,9 @@ fn par_quicksort<T: Ord + std::marker::Send>(slice: &mut [T]) {
return; return;
} }
let pivot = choose_pivot(slice); let pivot = partition(slice, choose_pivot(slice));
let pivot = partition(slice, pivot);
let (left_slice, right_slice) = slice.split_at_mut(pivot); let (left_slice, right_slice) = slice.split_at_mut(pivot);
// left_slice is [0 - pivot-1], right_slice is [pivot, end]. We don't want to include the let right_slice = &mut right_slice[1..]; // want to exclude pivot
// pivot, so reassign right_slice
let right_slice = &mut right_slice[1..];
join(|| quicksort(left_slice), || quicksort(right_slice)); join(|| quicksort(left_slice), || quicksort(right_slice));
} }
@ -132,3 +121,17 @@ fn qs(b: &mut Bencher) {
b.iter(|| quicksort(&mut test_vec)) b.iter(|| quicksort(&mut test_vec))
} }
#[test]
fn qs_comp() {
let bv = get_bench_vec();
let mut par = bv.clone();
let mut basic = bv.clone();
par_quicksort(&mut par);
quicksort(&mut basic);
for (l, r) in par.iter().zip(basic.iter()) {
assert_eq!(l, r)
}
}