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299. Bulls and Cows

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.

难度：medium

题目：你在和朋友玩bulls和cows游戏：你写下一个数字让你的朋友去猜。每次你的朋友猜一个数字，你给出提示有多少个数字值与位置相同（叫bulls)，有多少个数字值相同但位置不相同（叫cows)。你的朋友持续猜测直到获取正确的数字。

写一方法根据你朋友的猜测来返回提示，A表示bulls B表示cows.

思路：先找出所有精确匹配，然后单独统计值相同位置不相同的字符。

Runtime: 9 ms, faster than 21.94% of Java online submissions for Bulls and Cows.

Memory Usage: 35.6 MB, less than 78.72% of Java online submissions for Bulls and Cows.

class Solution {
    public String getHint(String secret, String guess) {
        int bulls = 0, cows = 0;
        int[] secretTable = new int[256];
        int[] guessTable = new int[256];
        for (int i = 0; i < secret.length(); i++) {
            if (secret.charAt(i) == guess.charAt(i)) {
                bulls++;
            } else {
                secretTable[secret.charAt(i)]++;
                guessTable[guess.charAt(i)]++;
            }
        }
        
        for (int i = 0; i < 256; i++) {
            cows += Math.min(secretTable[i], guessTable[i]);
        }
        
        return String.format("%dA%dB", bulls, cows);
    }
}

原文 https://segmentfault.com/a/1190000018314992

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