299. Bulls and Cows - LeetCode

from collections import Counter


class Solution:
    def getHint(self, s: str, g: str) -> str:
        a, b = 0, 0
        cs, cg = Counter(), Counter()
        for i in range(len(s)):
            if s[i] == g[i]:
                a += 1
                continue
            if cg[s[i]]:
                cg[s[i]] -= 1
                b += 1
            else:
                cs[s[i]] += 1
            if cs[g[i]]:
                cs[g[i]] -= 1
                b += 1
            else:
                cg[g[i]] += 1
        return f'{a}A{b}B'