[LeetCode] 389. Find the Difference

 Problem : https://leetcode.com/problems/find-the-difference/

Use hash table to find the difference:

class Solution:
    def findTheDifference(self, s: str, t: str) -> str:
        counterS = Counter(s)
        counterT = Counter(t)
        
        for k, v in counterT.items():
            if counterS[k] != v:
                return k