# LeetCode 1299. Replace Elements with Greatest Element on Right Side

## Description

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

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`

## Explanation

Just iterate the list and replace the elements as problem describes.

## Python Solution

``````class Solution:
def replaceElements(self, arr: List[int]) -> List[int]:
for i, num in enumerate(arr):
if i == len(arr) - 1:
arr[i] = -1
else:
arr[i] = max(arr[i + 1:])

return arr
``````
• Time Complexity: O(N).
• Space Complexity: O(N).