solutions/0202-happy-number.js

/**
 * 202. Happy Number
 * https://leetcode.com/problems/happy-number/
 * Difficulty: Easy
 *
 * Write an algorithm to determine if a number n is happy.
 *
 * A happy number is a number defined by the following process:
 * - Starting with any positive integer, replace the number by the sum of the squares of its digits.
 * - Repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a
 *   cycle which does not include 1.
 * - Those numbers for which this process ends in 1 are happy.
 *
 * Return true if n is a happy number, and false if not.
 */

/**
 * @param {number} n
 * @return {boolean}
 */
var isHappy = function(n) {
  while (n !== 1) {
    n = [...String(n)].reduce((sum, digit) => sum + digit ** 2, 0);
    if (n === 4) {
      return false;
    }
  }
  return true;
};