leetcode 299. Bulls and Cows

解题思路：
首先同时遍历一遍secret和guess，计算出Bulls，然后，以及不属于Bulls的字符及其出现的个数。然后遍历guess，利用第一次遍历时统计的信息，计算出cows
读懂题目意思，在计算cows时，对于重复数字，选取二者之间较小的一个

原题目：

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.

AC解，C++代码，菜鸟一个，请大家多多指正

class Solution {public:    string getHint(string secret, string guess) {        int bulls = 0;        map<char, int> sec_special;        for(string::size_type ix = 0; ix != secret.size(); ix++) {            if (secret[ix] == guess[ix]) {                bulls++;                guess[ix] = '#';            }            else {                sec_special[secret[ix]]++;            }        }        int cows = 0;        for(string::size_type ix = 0; ix != guess.size(); ix++) {            if (guess[ix] != '#') {                if (sec_special.count(guess[ix])) {                    cows ++;                    sec_special[guess[ix]]--;                    if(sec_special[guess[ix]] == 0) {                        sec_special.erase(guess[ix]);                    }                }            }        }        stringstream stream;        string ret;        string tmp;        stream << bulls;        stream >> tmp;        ret += tmp;        ret += "A";        stream.clear();        stream << cows;        stream >> tmp;        ret += tmp;        ret += "B";        return ret;    }};