Leetcode Length of Last Word

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(const char *s) {
        int len = strlen(s), cnt = 0;
        bool flag = false;
        for(int i = len-1; i >= 0 ; --i){
            if(s[i]!=' ') {flag =true;cnt++;}
            else if(flag) break;
        }
        return cnt;
    }
};