299. Bulls and Cows

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.

分析

遍历字符串，比较每个位是否相等，相等则记为bulls，否则在对应向量中将该位数字的记录+1，然后遍历两个向量，计算cows值，需要注意的是，虽然例子中给的cows为1，是因为secret中只有两个1，一个匹配为bulls，另一个匹配为cows，倘若secret为"1122"，guess为"2211"，则cows为4，因此cows计算中为v_s和v_g中的记录最小值之和。

class Solution {public:    string getHint(string secret, string guess) {        vector<int> v_s(10),v_g(10);        int bulls=0,cows=0;        for(int i=0;i<secret.size();i++)        {            if(secret[i]==guess[i])                bulls++;            else            {                v_s[secret[i]-48]++;                v_g[guess[i]-48]++;            }        }        for(int i=0;i<v_s.size();i++)        {            if(v_s[i]>0&&v_g[i]>0)                cows=cows+min(v_s[i],v_g[i]);        }        ostringstream os;        os<<bulls;        os<<'A';        os<<cows;        os<<'B';        return os.str();    }};

另：int返回为string还可以使用to_string()。