mergesort.rs

use rand::Rng;
use std::cmp::Ordering;

fn main() {
    let mut list: [i32; 1000] = [0; 1000];
    let mut helper: [i32; 1000] = [0; 1000];
    let mut rng = rand::thread_rng();
    for x in 0..1000 {
        list[x] = rng.gen_range(0..999);
    }

    for x in 0..1000 {
        println!("{}", list[x]);
    }
    println!("STOP");

    mergesort(&mut list, &mut helper, 0, 1000);
    for x in 0..1000 {
        println!("{}", list[x]);
    }
}

fn mergesort(list: &mut [i32; 1000], temp: &mut [i32; 1000], start: usize, end: usize) {
    if end - start <= 1 {
        return;
    }

    let mid = (end - start) / 2 + start;
    mergesort(list, temp, start, mid);
    mergesort(list, temp, mid, end);

    let mut l = start;
    let mut r = mid;
    for x in start..end {
        if r >= end {
            temp[x] = list[l];
            l += 1;
        } else if l >= mid {
            temp[x] = list[r];
            r += 1;
        } else {
            match list[l].cmp(&list[r]) {
                Ordering::Less => {
                    temp[x] = list[l];
                    l += 1;
                },
                Ordering::Greater => {
                    temp[x] = list[r];
                    r += 1;
                },
                Ordering::Equal => {
                    temp[x] = list[l];
                    l += 1;
                },
            }
        }
    }

    for x in start..end {
        list[x] = temp[x];
    }
}