58. Length of Last Word

Question
Given a string s consists of upper/lower-case alphabets and empty space characters ' ', return the length of last word in the string.
Input: "Hello World"
Output: 5

If the last word does not exist, return 0.

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

• first attempt

class Solution {
public:
    int lengthOfLastWord(string s) {
        if(s.size()==0)
            return 0;
        while(s.size()>0&&s.back()==' ')
            s.pop_back();
        int sum =0;
        string::reverse_iterator it;
        for(it=s.rbegin();it!=s.rend();it++)
        {
            if(*it==' ')
                return sum;
            else
                sum++;
        }
        return sum;       
    }
};