LeetCode -- Bulls and Cows

LeetCode -- Bulls and Cows

題目描述：


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.


給一個字符串s，包含了從0-9的數字。輸入一個字符串t，要求判斷t[j]和s[j]（j∈[0,N)）的每一位是否相等，如果相等，就看做是Bulls；如果不等，那麼就看t[j]是否等於s[i]，其中i!=j，如果等，就看做是cows。


1. 本題可以用哈希表來做，第一遍遍歷，將guess和secret的每一位比較，直接就能得出bulls的數量。同時統計s[i]的每一位出現的次數，存入哈希表hash中。
2. 如果bulls等於s的長度，說明secret和guess完全匹配，直接返回bulls即可。
3. 遍歷guess的每一位，如果guess在hash中出現並且hash[guess[i]]大於0，則hash[guess[i]]--,並統計cows的數量。
4. 最後返回bulls和cows的數量即可。




實現代碼：

public class Solution {
    public string GetHint(string secret, string guess) 
    {
        var bulls = 0;
    	var hash = new Dictionary();
    	for(var i = 0;i < secret.Length; i++){
    		if(guess[i] == secret[i]){
    			bulls++;
    		}
    		if(!hash.ContainsKey(secret[i])){
    			hash.Add(secret[i], 1);
    		}
    		else{
    			hash[secret[i]]++;
    		}
    	}
    	
    	if(bulls == secret.Length){
    		return string.Format({0}A0B,bulls);
    	}
    	
    	var guessed = 0;
    	for(var i = 0;i < guess.Length; i++){
    		if(hash.ContainsKey(guess[i]) && hash[guess[i]] > 0){
    			hash[guess[i]] --;
    			guessed ++;
    		}
    	}
    	
    	guessed -= bulls;
    	
    	return string.Format({0}A{1}B, bulls , guessed);
    }
}