2023-07-24 16:54:39 +0300 MSK

class Solution:
    def findTheDifference(self, s: str, t: str) -> str:
        letters = defaultdict(int)
        for letter in s:
            letters[letter] += 1

        for letter in t:
            if letters[letter] == 0:
                return letter
            
            letters[letter] -= 1
        
        return None