[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.

Solution:

class Solution {
public:
    int lengthOfLastWord(const char *s) {
        int len = 0;
        while(s[len] != '') len++;
        if(len == 0) return 0;
        
        int start = len - 1, end = len - 1;
        while(end >= 0 && s[end] == ' ') end--;
        if(end < 0) return 0;
        start = end - 1;
        while(start >= 0 && s[start] != ' ') start--;
        
        return end - start;
    }
};