void rvereseArray(int[] arr) {
    start = 0 
    end = arr.length - 1 
    while (start < end) {
        // swap arr[start] and arr[end]
        int temp = arr[start]
        arr[start] = arr[end]
        arr[end] = temp
        start = start + 1
        end = end - 1
    }
}