LeetCode C++ 1299. Replace Elements with Greatest Element on Right Side【Array】简单

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

题意：将给出的数组中，每个元素替换为右侧最大的元素，最后一个元素，用 -1 替换。

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思路：原地修改，从后往前替换数组元素，需要定义一个变量跟踪最大值。

代码：

class Solution {
public:
    vector<int> replaceElements(vector<int>& arr) { 
        if (arr.empty()) return arr;
        int maxValue = -1; 
        for (int i = arr.size() - 1; i >= 0; --i) { 
            int t = arr[i];
            arr[i] = maxValue;
            maxValue = max(maxValue, t);
        } 
        return arr;
    }
};