Replace Elements with Greatest Element on Right Side.md

[[Array & Hashing Questions (C)]]

Easy (12/10/2022)

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

Notes:

Question Name

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

Solution 1

    def replaceElements(self, arr: List[int]) -> List[int]:

        rightMax = -1

        for i in range(len(arr)-1, -1, -1):

            newMax = max(arr[i], rightMax)

            arr[i] = rightMax

            rightMax = newMax

        return arr