Replace Elements with Greatest Element on Right Side

https://leetcode.com/problems/replace-elements-with-greatest-element-on-right-side/

Question

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]

Answer

From here.

Iterate from the back to the start, We initilize mx = 1, where mx represent the max on the right. Each round, we set A[i] = mx, where mx is its mas on the right. Also we update mx = max(mx, A[i]), where A[i] is its original value.

class Solution:
    def replaceElements(self, arr: List[int]) -> List[int]:
        A = arr
        mx = -1
        for i in range(len(A) - 1, -1, -1):
            A[i], mx = mx, max(mx, A[i])
        return A