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 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".

You may assume that the secret number and your friend's guess only contain digits, and their lengths are always equal.

class Solution {
public:
    inline int min(int a, int b){
        return a > b? b : a;
    }
    string getHint(string secret, string guess) {
        set<int> bulls_pos;
        int bulls_cnt = 0, cows_cnt=0;
        int b1['9' + 1] = {0};
        int b2['9' + 1] = {0};
        
        for(int i=0;i<secret.size();i++){
            if(secret[i] == guess[i]){
                bulls_pos.insert(i);
                ++bulls_cnt;
            }
        }
        for(int i=0;i<secret.size();i++){
            if(bulls_pos.count(i) <= 0){
                b1[secret[i]] += 1;
                b2[guess[i]] += 1;
            }
        }
        for(int i='0'; i<='9';i++){
            cows_cnt += min(b1[i], b2[i]);
        }
        return to_string(bulls_cnt) + "A" + to_string(cows_cnt) + "B";
    }
};