Given an array `arr`, replace every element in that array with the greatest element among the elements to its right, and replace the last element with `-1`.

After doing so, return the array.

Example 1:

    Input: arr = [17,18,5,4,6,1]
    Output: [18,6,6,6,1,-1]
    Explanation:
    - index 0 --> the greatest element to the right of index 0 is index 1 (18).
    - index 1 --> the greatest element to the right of index 1 is index 4 (6).
    - index 2 --> the greatest element to the right of index 2 is index 4 (6).
    - index 3 --> the greatest element to the right of index 3 is index 4 (6).
    - index 4 --> the greatest element to the right of index 4 is index 5 (1).
    - index 5 --> there are no elements to the right of index 5, so we put -1.

Example 2:

    Input: arr = [400]
    Output: [-1]
    Explanation: There are no elements to the right of index 0.

Constraints:

- `1 <= arr.length <= 104`
- `1 <= arr[i] <= 105`