[leetcode][string] Length of Last Word

题目：

Given a string s consists of upper/lower-case alphabets and empty space characters ' ', return the length of last word in the string.

If the last word does not exist, return 0.

Note: A word is defined as a character sequence consists of non-space characters only.

For example, 
Given s = "Hello World",
return 5.

class Solution {public:    int lengthOfLastWord(string s) {        if(s.empty()) return 0;        int len = 0;        //转换为小写，便于判断        int i = -1;        while(s[++i]) s[i] = tolower(s[i]);        //过滤掉串尾的非字母字符        string::iterator iter = s.end()-1;        while(iter >= s.begin() && !(*iter >= 'a' && *iter <= 'z')) --iter;                while(iter >= s.begin() && *iter >= 'a' && *iter <= 'z'){            ++len;            --iter;        }        return len;    }};