题解 | #翻转单词序列#

常规实现，不用库函数

class Solution {
  public:
    string ReverseSentence(string str) {
      if (str.empty()) {
        return str;
      }
      
      int left = 0, right = 0;
      
      reverse_str(str, 0, str.size() - 1);
      
      while (right < str.size()) {
        while (right < str.size() && str[right] != ' ') {
          ++right;
        }
        reverse_str(str, left, right - 1);
        left = ++right;
      }
      
      return str;
    }
  private:
    void reverse_str(std::string &str, int left, int right) {
      if (str.empty()) {
        return ;
      }
      
      while (left < right) {
        char tmp = str[left];
        str[left] = str[right];
        str[right] = tmp;
        ++left, --right;
      }
    }
};