方法一：反向迭代器

int lengthOfLastWord(string s) {
        int count = 0;
        for(auto item = s.rbegin(); item != s.rend(); item++)
        {
            if(*item == ' ')
            {
                if(count == 0) count--;
                else   return count;
            }
            count++;
        }
        return count;
    }
 

方法二：while迴圈尋找 

  int lengthOfLastWord(string s) {
        int count = 0;
        if(s.size() == 0)
            return 0;
        int word_start = 0, word_end = 0;
        int i = s.size() - 1;
        while(i >= 0 & s[i] == ' ') --i;
        word_end = i;
        while(i >= 0 & s[i] != ' ') --i;
        word_start = i;
        return word_end - word_start;
    }