Bulls and Cows

class Solution {
    public String calculateHint(String secret, String guess) {
        HashMap<Character, Integer> mapCounter = new HashMap<>();
        
        int bullsCount = 0, cowsCount = 0;
        int length = guess.length();
        for (int i = 0; i < length; ++i) {
            char charSecret = secret.charAt(i);
            char charGuess = guess.charAt(i);
            if (charSecret == charGuess) {
                bullsCount++;    
            } else {
                if (mapCounter.getOrDefault(charSecret, 0) < 0) 
                    cowsCount++;
                if (mapCounter.getOrDefault(charGuess, 0) > 0)
                    cowsCount++;
                mapCounter.put(charSecret, mapCounter.getOrDefault(charSecret, 0) + 1);
                mapCounter.put(charGuess, mapCounter.getOrDefault(charGuess, 0) - 1);
            }
        } 
                
        return Integer.toString(bullsCount) + "A" + Integer.toString(cowsCount) + "B";
    }
}

The provided solution in Java aims to solve the "Bulls and Cows" game by determining how many bulls (correct digits in the correct position) and cows (correct digits but in the wrong position) a guess has relative to a secret number.

Here's a breakdown of the approach:

• A HashMap named mapCounter is introduced to store the frequency of characters that are not bulls, helping track the characters in both secret and guess.

• Two integer counters, bullsCount and cowsCount, are initialized to zero. They count the number of bulls and cows respectively.

• The algorithm iterates over each character of the secret and guess strings. If characters at the same index in both strings match, it increments the bullsCount.

• If they don't match, it uses the mapCounter to:

  • Decrement the count for characters from guess (indicating these characters need matches from secret).
  • Increment the count for characters from secret (indicating these characters need matches from guess).

  If after modifying the map:

  • A previously recorded character from secret now matches a character in guess (i.e., map value becomes less than zero), it increments the cowsCount.
  • A previously recorded character from guess now matches a character in secret (i.e., map value becomes positive), it also increments the cowsCount.

• Finally, the method returns the counts as a formatted string "{bullsCount}A{cowsCount}B", where A signifies the number of bulls and B signifies the number of cows.

By utilizing the HashMap to efficiently track the mismatches and later matches, this approach ensures the game logic is handled in a clear and concise manner without repetitively scanning arrays or strings. This makes the solution both efficient and straightforward to understand.

class Solution:
    def calculateHint(self, secret: str, guess: str) -> str:
        counts = defaultdict(int)
        bull_count = cow_count = 0

        for index, sec in enumerate(secret):
            gue = guess[index]
            if sec == gue:
                bull_count += 1
            else:
                cow_count += int(counts[sec] < 0) + int(counts[gue] > 0)
                counts[sec] += 1
                counts[gue] -= 1

        return f"{bull_count}A{cow_count}B"

This solution addresses the "Bulls and Cows" game using Python. In the game, you need to guess a secret string, where Bulls indicate correct characters in the right position, and Cows represent correct characters but in the wrong position.

• Initialize a dictionary counts to track the appearance of characters.
• Initialize two counters, bull_count and cow_count, to zero for tracking the number of Bulls and Cows respectively.
• Loop through the characters of both secret and guess strings simultaneously. Use enumerate for indexing.
• Compare each character of secret with the corresponding character in guess:
  • If they match, increment bull_count.
  • If they don't, update cow_count based on the conditions in the dictionary and adjust the dictionary counts accordingly:
    • Increment the count for the current secret character.
    • Decrement the count for the guessed character.
• Construct and return the result string formatted as "{bull_count}A{cow_count}B".

This approach effectively counts both Bulls directly and uses the appearance dictionary to determine Cows by considering character frequencies across different indices. Ensure understanding and utilizing collections such as defaultdict to handle the counting logic efficiently.