Merge-sort implementation in Rust

merge_sort.rs

fn mergesort(unsorted: &[u32]) -> Vec<u32> {
    let n = unsorted.len();
    if n < 2 {
        return unsorted.to_vec();
    }
    let sorted_child1 = mergesort(&unsorted[..n/2]);
    let sorted_child2 = mergesort(&unsorted[n/2..]);
    let mut ptr1 = 0;
    let mut ptr2 = 0;
    let mut sorted = vec![];
    for _ in 0..n {
        if ptr1 >= sorted_child1.len() {
            sorted.push(sorted_child2[ptr2]);
            ptr2 += 1;
        } else if ptr2 >= sorted_child2.len() {
            sorted.push(sorted_child1[ptr1]);
            ptr1 += 1;
        } else if sorted_child1[ptr1] <= sorted_child2[ptr2] {
            sorted.push(sorted_child1[ptr1]);
            ptr1 += 1;
        } else {
            sorted.push(sorted_child2[ptr2]);
            ptr2 += 1;
        }
    }
    sorted
}


#[test]
fn test_mergesort() {
    let unsorted_array = [3, 7, 2, 5, 9, 1, 5, 7, 2, 98, 32, 6, 4];
    assert_eq!(vec![1, 2, 2, 3, 4, 5, 5, 6, 7, 7, 9, 32, 98], mergesort(&unsorted_array));
}