Leetcode 1299. Replace Elements with Greatest Element on Right Side

Posted 2021-09-05 SnailTyan

文章作者：Tyan
博客：noahsnail.com  |  CSDN  |  简书

1. Description

2. Solution

**解析：**Version 1，先排序获取索引，从最大值所在的索引开始遍历，只要是其左侧没有更新过的值都更新，使用left来确定范围，left始终是已更新数据的最右侧，其是下一次遍历的左边界。Version 2从倒数第二个元素开始向前遍历，maximum用来保存右侧最大值，每次遍历先更新当前索引结果位置的数值为maximum，然后更新maximum。

• Version 1

class Solution:
    def replaceElements(self, arr: List[int]) -> List[int]:
        n = len(arr)
        result = [-1] * n
        indexes = sorted(range(n), key=lambda i: arr[i], reverse=True)
        left = 0
        for i in range(n):
            index = indexes[i]
            for j in range(left, index):
                result[j] = arr[index]
            left = max(left, index)
        return result

• Version 2

class Solution:
    def replaceElements(self, arr: List[int]) -> List[int]:
        n = len(arr)
        result = [-1] * n
        maximum = arr[-1]
        i = n - 2
        while i > -1:
            result[i] = maximum
            maximum = max(maximum, arr[i])
            i -= 1
        return result

Reference

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