299. Bulls and Cows

题目摘要
给出两个数字，猜第二个数字与第一个数字大小和位置完全相等位的个数，和大小相等位置不同的个数，以“1A2B”的形式返回。

解法
1. hashTable(不推荐)，因为数据规模很小，只有10个数字
2. 用两个数组（最好）

public String getHint(String secret, String guess) {        int[] s = new int[10];        int[] g = new int[10];        int bulls = 0;        int cows = 0;        for (int i = 0; i < secret.length(); i++) {            if (secret.charAt(i) == guess.charAt(i)) {                bulls++;            } else {                s[secret.charAt(i) - '0']++;                g[guess.charAt(i) - '0']++;            }        }        for (int i = 0; i < 10; i++) {            cows += Math.min(s[i], g[i]);        }        return bulls + "A" + cows + "B";    }

1. 用一个数组

public String getHint(String secret, String guess) {    int bulls = 0;    int cows = 0;    int[] numbers = new int[10];    for (int i = 0; i<secret.length(); i++) {        if (secret.charAt(i) == guess.charAt(i)) bulls++;        else {            if (numbers[secret.charAt(i)-'0']++ < 0) cows++;            if (numbers[guess.charAt(i)-'0']-- > 0) cows++;        }    }    return bulls + "A" + cows + "B";}

注意

可问问题
* 两个数字位数相不相同

原题
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, for example:

Secret number: “1123”
Friend’s guess: “0111”

In this case, the 1st 1 in friend’s guess is a bull, the 2nd or 3rd 1 is a cow, and your function should return "1A1B".
You may assume that the secret number and your friend’s guess only contain digits, and their lengths are always equal.