# 1299. Replace Elements with Greatest Element on Right Side

Easy
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`

### 解題

Runtime: 17 ms, faster than 88.89%
Memory Usage: 6.3 MB, less than 88.00%
func replaceElements(arr []int) []int {
max := -1
for i:= len(arr)-1; i>=0; i-- {
tmp := max
if arr[i] > max { max = arr[i] }
arr[i] = tmp
}
return arr
}