mergesort.rs

extern crate rand;
use rand::Rng;
use std::time::Instant;

fn merge(l1: &Vec<i32>, s: usize, m: usize, e: usize, l2: &mut Vec<i32>) {
    let mut ptr1 = s;
    let mut ptr2 = m;

    for i in s..e {
        if (ptr1 < m) && (ptr2 >= e || l1[ptr1] <= l1[ptr2]) {
            l2[i] = l1[ptr1];
            ptr1 += 1;
        } else {
            l2[i] = l1[ptr2];
            ptr2 += 1;
        }
    }
}

fn merge_copy(l1: &mut Vec<i32>, s: usize, e: usize, l2: &Vec<i32>) {
    (s..e).for_each(|i| l1[i] = l2[i]);
}

fn merge_split(l1: &mut Vec<i32>, s: usize, e: usize, l2: &mut Vec<i32>) {
    if e - s > 1 {
        let m: usize = (e + s) / 2;

        merge_split(l1, s, m, l2);
        merge_split(l1, m, e, l2);
        merge(l1, s, m, e, l2);
        merge_copy(l1, s, e, l2);
    }
}

pub fn merge_sort(l: &mut Vec<i32>) {
    let size: usize = l.len();
    let mut worker: Vec<i32> = vec![0; size];

    merge_split(l, 0, size, &mut worker);
}


fn main() {
  let mut rng = rand::thread_rng();
  let mut numbers: Vec<i32> = (0..1000000).map(|_| {
      rng.gen_range(1, 1000000)
  }).collect();

  let start = Instant::now();
  merge_sort(&mut numbers);
  let elapsed = start.elapsed();

  println!("{}", numbers[0]);
  println!("{:?}", elapsed);
}