Find the Difference Solutions in C++

// Source : https://leetcode.com/problems/find-the-difference/
// Author : Hao Chen
// Date   : 2016-09-08



class Solution {
public:
    char findTheDifference(string s, string t) {
        unordered_map<char, int> m;
        for(auto c : s) m[c]++;
        for(auto c : t) {
            m[c]--;
            if (m[c] < 0) return c;
        }
        return '\0';
    }
};

/// Source : https://leetcode.com/problems/find-the-difference/description/
/// Author : liuyubobobo
/// Time   : 2017-10-27

#include <iostream>
#include <string>
#include <cassert>
using namespace std;

class Solution {
public:
    char findTheDifference(string s, string t) {

        if(s.size() == 0){
            assert(t.size() == 1);
            return t[0];
        }

        char res = s[0];
        for(int i = 1 ; i < s.size() ; i ++)
            res ^= s[i];
        for(int i = 0 ; i < t.size() ; i ++)
            res ^= t[i];

        return res;
    }
};

int main() {

    string s = "abcd";
    string t = "abcde";
    cout << Solution().findTheDifference(s, t) << endl;

    return 0;
}