Playing the Bulls and Cows Game in Java

The challenge

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.

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. 

Please note that both secret number and friend’s guess may contain duplicate digits.

Example 1:

Input: secret = "1807", guess = "7810"
Output: "1A3B"
Explanation: 1 bull and 3 cows. The bull is 8, the cows are 0, 1 and 7.

Example 2:

Input: secret = "1123", guess = "0111"
Output: "1A1B"
Explanation: The 1st 1 in friend's guess is a bull, the 2nd or 3rd 1 is a cow.

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

The solution in Java

class Solution { public String getHint(String secret, String guess) { // keep counts int bulls=0; int cows =0; // keep primitive arrays int[] secretArr1 = new int[10]; int[] guessArr2 = new int[10]; // loop through the secret for(int i=0; i<secret.length(); i++){ // get the current characters char c1 = secret.charAt(i); char c2 = guess.charAt(i); // if they match, then increment bulls if(c1==c2) bulls++; else{ // otherwise increment our arrays secretArr1[c1-'0']++; guessArr2[c2-'0']++; } } // loop through our primitive arrays for(int i=0; i<10; i++){ // increment our cows according to which primitive is smaller cows += Math.min(secretArr1[i], guessArr2[i]); } // return the answer return bulls+"A"+cows+"B"; } }
Code language: Java (java)
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