# 问题 原题链接：[https://leetcode.com/problems/reverse-words-in-a-string-ii/](https://leetcode.com/problems/reverse-words-in-a-string-ii/) Given an input string , reverse the string word by word. Example: ``` Input: ["t","h","e"," ","s","k","y"," ","i","s"," ","b","l","u","e"] Output: ["b","l","u","e"," ","i","s"," ","s","k","y"," ","t","h","e"] ``` Note: - A word is defined as a sequence of non-space characters. - The input string does not contain leading or trailing spaces. - The words are always separated by a single space. Follow up: - Could you do it in-place without allocating extra space? # 分析过程 - 输入：字母和空格组成的字符串 - 输出：反转字符串内容，但单词内容不反转 - 思路：将整个字符串翻转一遍，然后再次翻转每个单词 # 解决方法 ```cpp class Solution { public: void reverse(vector<char>& str, int begin, int end) { if (end <= begin) { return; } int low = begin, high = end; while (low < high) { char tmp = str[low]; str[low] = str[high]; str[high] = tmp; ++low; --high; } } void reverseWords(vector<char>& str) { int len = (int)str.size(); if (len <= 0) { return; } // 先把所有字符翻转一遍 reverse(str, 0, len - 1); // 然后开始扫描空格 int begin = 0; for (int i = 0; i < len; i++) { // 扫到空格以后，逆转 begin 到 i if (str[i] == ' ') { reverse(str, begin, i - 1); begin = i + 1; } } // 翻转最后一个单词 reverse(str, begin, len - 1); } }; ```