Rust implementation of Merge Sort algorithm from CLRS book

merge_sort.rs

fn merge(a: &mut Vec<i32>, p: usize, q: usize, r: usize) {
  let al = [&a[p..=q], &[i32::MAX]].concat();
  let ar = [&a[q+1..=r], &[i32::MAX]].concat();
  let mut i = 0;
  let mut j = 0;
  for k in p..=r {
    if al[i] <= ar[j] {
      a[k] = al[i];
      i += 1;
    } else {
      a[k] = ar[j];
      j += 1;
    }
  }
}

fn merge_sort(a: &mut Vec<i32>, p: usize, r: usize) {
  if p < r {
    let q = (p + r) / 2;
    merge_sort(a, p, q);
    merge_sort(a, q + 1, r);
    merge(a, p, q, r);
  }
}

fn main() {
  let mut n = vec![1,5,8,9,2,4,7,9];
  let len = n.len();
  merge_sort(&mut n, 0, len-1);
  println!("{:?}", n);
}