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) {
        int sum = t[s.length()];
        for(int i=0; i<s.length(); i++)
            sum += t[i]-s[i];
        return (char)sum;
    }
};