Mergesort in Rust translated from a Python implementation

main.rs

// Mergesort implementation in Rust translated from the Python example at 
// https://www.interviewbit.com/tutorial/merge-sort-algorithm/

fn main () {
    println!(".......Mergesort");

    let unsorted : [i32; 10] = [949, 8232, 158, 369, 1, 43, 949, 381112, 4184, 12];
    let mut arr : Vec<i32> = unsorted.to_vec();
    println!("arr at beginning, {:?}", arr);
    let start : usize = 0;
    
    let end : usize = 9;

    merge_sort(&mut arr, start, end);

    println!("arr at end, {:?}", arr);

}



//  example of merge sort in Python
// merge function take two intervals
// one from start to mid
// second from mid+1, to end
// and merge them in sorted order
fn merge(
    arr: &mut Vec<i32>,
    start: usize,
    mid: usize,
    end: usize
    ) -> &mut Vec<i32> {


    // create a temp array
    let mut temp : Vec<i32> = vec![0; (end - start) + 1 ];


    // crawlers for both intervals and for temp
    let mut i : usize = start;
    let mut j : usize = mid + 1;
    let mut k : usize = 0;


    // traverse both lists and in each iteration add smaller of both elements in temp
    while (i <= mid) && (j <= end) {
        if arr[i] <= arr[j] {
            temp[k] = arr[i];
            k +=1; i += 1;
        } else {
            temp[k] = arr[j];
            k += 1; j += 1;
        }
    }

    // add elements left in the first interval 
    while i <= mid {
        temp[k] = arr[i];
        k += 1;
        i += 1;
    }

    // add elements left in the second interval 
    while j <= end {
        temp[k] = arr[j];
        k += 1;
        j += 1;
    }

    // copy temp to original interval
    for i in start..end + 1 {
        arr[i] = temp[i - start];
    }
    arr
}


fn merge_sort (
    arr: &mut Vec<i32>,
    start: usize,
    end: usize
    ) -> &mut Vec<i32> {

    if start < end {
        let mid: usize = (start + end) / 2;
        merge_sort(arr, start, mid);
        merge_sort(arr, mid + 1, end);
        merge(arr, start, mid, end);
    }
    arr
}