leetcode299. Bulls and Cows

299. Bulls and Cows

问题描述：

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 are0, 1 and 7.)

Write a function to return a hint according to the secret number and friend's guess, useA 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.

解析：

/*同时遍历两个字符串，当相同位置上的字符相同时，bulls++ * 当相同位置上的字符不同时： *    s串上的nums[s]++； *    g串上的nums[g]--； * 这样，在遇到字符不相同的情况时，先判断该位置上的nums[s]是否小于0,小于0说明在g串中出现过，cows++; * 该位置上的nums[g]是否大于0，如果大于0说明在s串中出现过，那么cow++;**/
public String getHint(String secret, String guess) {        int bulls=0;int cows=0;int[] nums=new int[10];for(int i=0;i<secret.length();i++){int s=Character.getNumericValue(secret.charAt(i));int g=Character.getNumericValue(guess.charAt(i));if(s==g) bulls++;else{if(nums[s]<0) cows++;if(nums[g]>0) cows++;nums[s]++;nums[g]--;}}return bulls+"A"+cows+"B";    }