quick sort 2 way & 3 way

qsort.rs

use std::cmp::Ordering;

fn qsort3way<T: Ord + Copy>(sli: &mut [T], lo: usize, hi: usize) {
    if hi <= lo {return;}
    let mut lt = lo;
    let mut i = lt + 1;
    let mut gt = hi;
    let v = sli[lo];
    while i <= gt {
        match sli[i].cmp(&v) {
            Ordering::Less => {
                sli.swap(lt, i);
                i += 1;
                lt += 1;
            },
            Ordering::Equal => {
                i += 1;
            },
            Ordering::Greater => {
                sli.swap(gt, i);
                gt -= 1;
            }
        }
    }
    qsort3way(sli, lo, lt - 1);
    qsort3way(sli, gt + 1, hi);
}
fn kth<T: Ord + Clone>(sli: &mut [T], k:usize, lo: usize, hi: usize) -> Option<usize>{
    if hi <= lo {return None;}
    let mut i = lo + 1;
    let mut j = hi;
    let pivot = sli[lo].clone();
    loop {
        while sli[i] < pivot {
            if i == hi {break;}
            i += 1;
        }
        while pivot < sli[j] {
            j -= 1;
        }
        if i >= j {break;}
        sli.swap(i, j);
    }
    sli.swap(lo, j);
    match k.cmp(&j) {
        Ordering::Less => {
            kth(sli, k + 1, lo, j - 1)
        },
        Ordering::Equal => {
            Some(j)
        },
        Ordering::Greater => {
            kth(sli, k - j - 1, j + 1, hi)
        }
    }

}
fn qsort2way<T: Ord + Copy>(sli: &mut [T], lo: usize, hi: usize) {
    if hi <= lo {return;}
    let mut i = lo + 1;
    let mut j = hi;
    let pivot = sli[lo];
    loop {
        while sli[i] < pivot {
            if i == hi {break;}
            i += 1;
        }
        while pivot < sli[j] {
            if j == lo {break;}
            j -= 1;
        }
        if i >= j {break;}
        sli.swap(i, j);
    }
    sli.swap(lo, j);
    if j > 0 {qsort2way(sli, lo, j - 1);}
    qsort2way(sli, j + 1, hi);
}
fn main() {
    let ref mut s = [3,6,7,8,5,4,1,2];
    println!("{:?}", kth(s, 0, 0, 7));
    println!("{:?}", s);
}