binary-watch.js

/**
 * Binary Watch
 *
 * A binary watch has 4 LEDs on the top which represent the hours (0-11),
 * and the 6 LEDs on the bottom represent the minutes (0-59).
 *
 * Each LED represents a zero or one, with the least significant bit on the right.
 *
 * For example, the above binary watch reads "3:25".
 *
 * Given a non-negative integer n which represents the number of LEDs that are currently on,
 * return all possible times the  * watch could represent.
 *
 * Example:
 *
 * Input: n = 1
 * Return: ["1:00", "2:00", "4:00", "8:00", "0:01", "0:02", "0:04", "0:08", "0:16", "0:32"]
 * Note:
 * The order of output does not matter.
 * The hour must not contain a leading zero, for example "01:00" is not valid, it should be "1:00".
 * The minute must be consist of two digits and may contain a leading zero,
 * for example "10:2" is not valid, it should be "10:02".
 */

/**
 * @param {number} num
 * @return {string[]}
 */
const readBinaryWatch = num => {
  const result = [];

  for (let h = 0; h < 12; h++) {
    for (let m = 0; m < 60; m++) {
      if (hammingWeight(h * 64 + m) === num) {
        result.push(`${h}:${m < 10 ? '0' + m : m}`);
      }
    }
  }

  return result;
};

const hammingWeight = n => {
  let count = 0;
  for (let i = 0; i < 32; i++) {
    if ((n & 1) !== 0) count++;
    n >>= 1;
  }
  return count;
};

export { readBinaryWatch };