leetcode 389. Find the Difference

class Solution {
public:
    char findTheDifference(string s, string t) {
        int x[26]={0};
        for(int i = 0;i < s.length(); i++)
            x[s[i]-'a']++;
        for(int i = 0;i < t.length(); i++)
            x[t[i]-'a'] --;
        for(int i = 0;i < 26;i++)
            if(x[i] != 0)
                return i+'a'; 
        return '0';
    }
};