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]
Constraints:
<li><code>1 <= arr.length <= 10^4</code></li>
<li><code>1 <= arr[i] <= 10^5</code></li>