leetcode 389. Find the Difference

Given two strings s and t which consist of only lowercase letters.

String t is generated by random shuffling string s and then add one more letter at a random position.

Find the letter that was added in t.

Example:

Input:
s = "abcd"
t = "abcde"

Output:
e

Explanation:
'e' is the letter that was added.

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