How to write the Bulls and Cows code in Java

The Cows and Bulls Game

The Cows and Bulls game is an old game that asks each person to guess a number. Each incorrect guess returns a hint and each hint consists of the numbers of bulls and cows in the guess. A bull is the correct digit in the correct position. A cow is the correct digit in the wrong position. For example, if the secret number is 2045, and the guess is 5248, the hint would be that the guess has 1 bull (4) and 2 cows (5 and 2).

import java.io.File;
import java.util.Scanner;
import java.io.FileNotFoundException;
class CowAndBull {
  public static String hint(String secret, String guess){
    // Initializing count variables
    int bullCount = 0;
    int cowCount = 0;
    // Initializing arrays
    // Each array contains the count for each digit
    // at its corresponding index
    int []secDigitCount = new int[10];
    int []guessDigitCount = new int[10];
    for (int i = 0; i < Math.min(secret.length(), guess.length()); i++){
      // Getting characters
      char secretChar = secret.charAt(i);
      char guessChar = guess.charAt(i);
      if (secretChar == guessChar){
        // Incrementing bull count
        bullCount += 1;
      }
      else {
        // Incrementing digit counts
        secDigitCount[secretChar - '0'] += 1;
        guessDigitCount[guessChar - '0'] += 1;
      }
    }
    // If statements and loops to handle remaining 
    // characters in case of string length differences
    if (secret.length() > guess.length()){
      for (int i = guess.length(); i < secret.length(); i++){
        secDigitCount[secret.charAt(i) - '0'] += 1;
      }
    }
    else if (secret.length() < guess.length()){
      for (int i = secret.length(); i < guess.length(); i++){
        guessDigitCount[guess.charAt(i) - '0'] += 1;
      }
    }
    // Loop to count Cows
    for (int i = 0; i < 10; i++){
      cowCount += Math.min(secDigitCount[i], guessDigitCount[i]);
    }
    return bullCount + " Bulls, " + cowCount + " Cows";
  }
  public static void main( String args[] ) {
    // File reading for input
    try{
      File myObj = new File("__ed_input.txt");
      Scanner inReader = new Scanner(myObj);
      String secret = inReader.nextLine();
      // Loop for all guesses in input file
      String guess;
      while(inReader.hasNextLine()){
        guess = inReader.nextLine();
        System.out.println(hint(secret, guess));
      }
      inReader.close();
    }
    catch (FileNotFoundException e) {
      System.out.println("An error occurred.");
    }
  }
}

Enter the input below to be saved in file __ed_input.txt

Code input area

The hint() function generates a hint for each input. The first for loop runs equal to the number of digits in either secret or guess, whichever is smaller. This loop traverses the characters and compares them at each index. For every match, the bull-count goes up.

To count cows, the program counts every digit in secret and guess that do not form a bull-pair. Two arrays, secDigitCount and guessDigitCount, are defined. These arrays store the count for each digit at its respective index. For instance, secDigitCount[4] contains the number of 4s in the secret. The value assignments for these arrays use the indexing expression [character - '0'] to transpose the converted ASCII digit values into their corresponding integers.

The if statements following the first loop count the remaining digits for the larger string out of secret and guess if string sizes differ. In the last for loop, the cows are incremented. The min function is applied to take care of duplicate digits in the secret or guess. For instance, if the secret is 2045 and the guess is 3225, the number of cows should be 1, not 2.

How to write the Bulls and Cows code in Java

The Cows and Bulls Game

Solution