LeetCode 151. Reverse Words in a String

1. 句子开头和末尾的空格要去掉

2. 单词间的多个空格要变为一个空格

代码：

void reverseWords(string &s) {string s2;bool first = true;for (size_t i = 0; i < s.size(); ++ i){int begin, end;for ( ; i < s.size() && s[i] == ' '; ++ i ) {}begin = i;for ( ; i < s.size() && s[i] != ' '; ++ i) {}end = i;if (begin == s.size()){break;}if (first == true){s2.insert(0, s.substr(begin, end-begin));first =  false;} else{s2.insert(0, " ");s2.insert(0, s.substr(begin, end-begin));}}s = s2;}