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0299. Bulls and Cows.md

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题目

You are playing the following Bulls and Cows game with your friend: You write down a number and ask your friend to guess what the number is. Each time your friend makes a guess, you provide a hint that indicates how many digits in said guess match your secret number exactly in both digit and position (called "bulls") and how many digits match the secret number but locate in the wrong position (called "cows"). Your friend will use successive guesses and hints to eventually derive the secret number.

Write a function to return a hint according to the secret number and friend's guess, use A to indicate the bulls and B to indicate the cows.

Please note that both secret number and friend's guess may contain duplicate digits.

Example 1:

Input: secret = "1807", guess = "7810"

Output: "1A3B"

Explanation: 1 bull and 3 cows. The bull is 8, the cows are 0, 1 and 7.

Example 2:

Input: secret = "1123", guess = "0111"

Output: "1A1B"

Explanation: The 1st 1 in friend's guess is a bull, the 2nd or 3rd 1 is a cow.

Note: You may assume that the secret number and your friend's guess only contain digits, and their lengths are always equal.

我的思路

题目给了一个secret字符串和一个guess字符串，长度相等。如果对应位置猜对了，那么就称之为一个bull；如果某个位置猜的字符没有猜对，但是这个猜的字符在其他位置出现了，称之为一个cow。题目要求我们统计有多少个bull和cow。

bull直接循环即可计算出来；cows比较麻烦，需要建立两个字典分别存储两个字符串中出现的词频。若出现了相同字符，取两个字典中较小的那一个值。最后需要在cows中减去bull，防止重复计算。

class Solution:
    def getHint(self, secret: str, guess: str) -> str:
        bull, cows = 0, 0
        dic1 = Counter(secret)
        dic2 = Counter(guess)
        for i in range(len(secret)):
            if secret[i] == guess[i]:
                bull += 1
        for x in dic1:
            if x in dic2.keys():
                cows += min(dic1[x],dic2[x])
        cows -= bull
        return str(bull)+"A"+str(cows)+"B"