[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 = 0, tail = s.length() - 1;
        while (tail >= 0 && s[tail] == ' ') tail--;
        while (tail >= 0 && s[tail] != ' ') {
            len++;
            tail--;
        }
        return len;
    }
};