LeetCode //C - 299. Bulls and Cows

299. Bulls and Cows

You are playing the Bulls and Cows game with your friend.

You write down a secret number and ask your friend to guess what the number is. When your friend makes a guess, you provide a hint with the following info:

• The number of “bulls”, which are digits in the guess that are in the correct position.
• The number of “cows”, which are digits in the guess that are in your secret number but are located in the wrong position. Specifically, the non-bull digits in the guess that could be rearranged such that they become bulls.

Given the secret number secret and your friend’s guess guess, return the hint for your friend’s guess.

The hint should be formatted as “xAyB”, where x is the number of bulls and y is the number of cows. Note that both secret and guess may contain duplicate digits.
 

Example 1:

Input: secret = “1807”, guess = “7810”
Output: “1A3B”
Explanation: Bulls are connected with a ‘|’ and cows are underlined:
“1807”
|
“7810”

Example 2:

Input: secret = “1123”, guess = “0111”
Output: “1A1B”
Explanation: Bulls are connected with a ‘|’ and cows are underlined:
“1123” “1123”
| or |
“0111” “0111”
Note that only one of the two unmatched 1s is counted as a cow since the non-bull digits can only be rearranged to allow one 1 to be a bull.

Constraints:

• 1 <= secret.length, guess.length <= 1000
• secret.length == guess.length
• secret and guess consist of digits only.

From: LeetCode
Link: 299. Bulls and Cows

Solution:

Ideas:

• Counting Bulls: The loop iterates over the characters of secret and guess strings and increments the bulls counter whenever the characters match.

• Tracking Unmatched Digits: For digits that do not match, we increase the count of those digits in both the secret_count and guess_count arrays. The index in these arrays corresponds to the digit itself (i.e., the character ‘0’ maps to index 0, ‘1’ maps to index 1, and so on).

• Counting Cows: After iterating through all characters, we compute the cows by taking the minimum count of each digit in both the secret_count and guess_count arrays. This ensures we count each digit correctly as a cow only as many times as it appears in both the secret and the guess.

• Formatting Result: We use sprintf to format the output string as “xAyB” and return it.

Code:

char* getHint(char* secret, char* guess) {
    int bulls = 0, cows = 0;
    int secret_count[10] = {0};
    int guess_count[10] = {0};
    int length = strlen(secret);

    // First pass: count bulls
    for (int i = 0; i < length; i++) {
        if (secret[i] == guess[i]) {
            bulls++;
        } else {
            // Count unmatched digits
            secret_count[secret[i] - '0']++;
            guess_count[guess[i] - '0']++;
        }
    }

    // Second pass: count cows
    for (int i = 0; i < 10; i++) {
        cows += (secret_count[i] < guess_count[i]) ? secret_count[i] : guess_count[i];
    }

    // Prepare the result in the format "xAyB"
    char* result = (char*)malloc(10 * sizeof(char)); // Allocate enough space for the result
    sprintf(result, "%dA%dB", bulls, cows);
    return result;
}