1299. Replace Elements with Greatest Element on Right Side

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

Description

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

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