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:
    def findTheDifference(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: str
        """
        if len(t)>len(s):
            s,t = t,s
        a = list(s)
        b = {}
        for i in t:
            if i in b:
                b[i] += 1
            else:
                b[i] = 1
        for i in a:
            if i not in b:
                return i
            if b[i]==0:
                return i
            b[i] -= 1