题目如下：

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]

Constraints:

• 1 <= arr.length <= 10^4
• 1 <= arr[i] <= 10^5

解题思路：从右往左遍历arr，同时记录出现的最大值即可。

代码如下：

class Solution(object):
    def replaceElements(self, arr):
        """
        :type arr: List[int]
        :rtype: List[int]
        """
        res = [-1]
        max_val = arr[-1]
        for i in range(len(arr)-2,-1,-1):
            res.insert(0,max_val)
            max_val = max(arr[i], max_val)
        return res