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

class Solution(object):
    def findTheDifference(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: str
        """
        letters={}
        for c in s:
            letters[c]=letters[c]+1 if c in letters else 1
        for c in t:
            if(c not in letters):
                return c
            letters[c]=letters[c]-1
            if letters[c]<0:
                return c