Bull And Cows

Question Description

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.

For example:

Secret number: "1807"

Friend's guess: "7810"

Hint: 1 bull and 3 cows. (The bull is 8, the cows are 0, 1 and 7.)

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. In the above example, your function should return "1A3B".

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

Solution

For both the guess and secret string, we check the digits one by one.

If they are equal, we just add one to the number of 'A'.

If not, we will check the number of digits for secret[i], if it is smaller than 0, we know that there must be some char in guess that is equal to it, so we add one to the number of 'B'; at the same time, it works similar for checking number of guess[i].

Then we get the final result.

class Solution(object):
    def getHint(self, secret, guess):
        """
        :type secret: str
        :type guess: str
        :rtype: str
        """
        letters, a, b= [0 for x in range(10)], 0, 0
        for i in range(len(secret)):
            if secret[i] == guess[i]:
                a += 1
            else:
                s, g = int(secret[i]), int(guess[i])
                if letters[s] < 0:
                    b += 1
                letters[s] += 1
                if letters[g] > 0:
                    b += 1
                letters[g] -= 1
        return str(a) + 'A' + str(b) + 'B'