leetcocd_Bulls and Cows

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 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.

思路：

这一题求的不是两个字符串之间字符跟字符的对应关系，也不是字符和单词的对应关系，本题求的是两个字符串在相同的位置上有多少字符是相同的，剩下的退而求其次，不同的字符有多少个位置虽然不同但字符是相同的。这个可以通过维持一个统计26个字符出现次数的数组来实现，先统计一个字符串中跟另一个字符串同一位置不相同的字符出现的次数，然后在统计另外一个字符串中同一位置不相同的字符出现的次数，通过相减除去同一位置不相同字符的次数， 同时统计出现的出去相同位置字符相同的情况的其它不同位置相同字符的个数，即可统计出两外的cow数量。

代码：

public String getHint(String secret, String guess) {
        int strLen=secret.length();
        int countArr[]=new int[10];
        int bullCount=0,cowCount=0;
        char chSecret,chGuess;
        for(int i=0;i<strLen;i++)
        {
            chSecret=secret.charAt(i);
            chGuess=guess.charAt(i);
            if(chSecret==chGuess)
                bullCount++;
            else
                countArr[chSecret-'0']++;
        }
        int index=0;
        for(int i=0;i<strLen;i++)
        {
            chSecret=secret.charAt(i);
            chGuess=guess.charAt(i);
            if(chSecret!=chGuess)
            {
                index=chGuess-'0';
                if(countArr[index]>0)
                {
                    countArr[index]--;
                    cowCount++;
                }
            }
        }
        return ""+bullCount+"A"+cowCount+"B";
    }