bulls-and-cows.js

/**
 * Bulls and Cows
 *
 * 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.
 */

/**
 * @param {string} secret
 * @param {string} guess
 * @return {string}
 */
const getHint = (secret, guess) => {
  let bulls = 0;
  let cows = 0;

  const count = Array(10).fill(0);

  for (let i = 0; i < secret.length; i++) {
    if (secret[i] === guess[i]) {
      bulls++;
    } else {
      if (count[secret[i] - '0'] < 0) cows++;
      if (count[guess[i] - '0'] > 0) cows++;

      count[secret[i] - '0']++;
      count[guess[i] - '0']--;
    }
  }

  return `${bulls}A${cows}B`;
};

export { getHint };