[LintCode] 最后一个单词的长度

 class Solution {
 public:
     /**
      * @param s A string
      * @return the length of last word
      */
     int lengthOfLastWord(string s) {
         int len = , tail = s.length() - ;
         while (tail >=  && s[tail] == ' ') tail--;
         while (tail >=  && s[tail] != ' ') {
             len++;
             tail--;
         }
         return len;
     }
 };