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.

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.

Credits:
Special thanks to @jeantimex for adding this problem and creating all test cases.

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题目的意思就是求有多少个位置和字符都正确的字符（bulls个），还有多少个字符正确但位置不正确的字符（cows个）。求bulls直接遍历一遍一一对比就能知道有多少个。在遍历时，对非一致的字符作计数。求cows时，取两个字符串各个字符计数值小的那个值，进行累加即可。

代码:

class Solution {public:    string getHint(string secret, string guess) {        int bulls = 0, cows = 0;        int scnt[10] = {0}, gcnt[10] = {0};        for(int i = 0; i < secret.size(); ++i) {            if(secret[i] == guess[i]) {                bulls += 1;            }            else {                ++scnt[secret[i]-'0'];                ++gcnt[guess[i]-'0'];            }        }        for(int i = 0; i <= 9; ++i) {            cows += min(scnt[i], gcnt[i]);        }        return to_string(bulls)+"A"+to_string(cows)+"B";    }};