202. Happy Number

Description

Write an algorithm to determine if a number 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, and 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 numbers.

Example: 19 is a happy number

12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

Solution

/**
 * Solved with hash table
 * @param {number} n
 * @return {boolean}
 */
var isHappy = function(n) {
    "use strict";
    let table = {};
    while (n !== 1) {
        if (table[n] === undefined) {
            table[n] = true;
        } else {
            return false;
        }
        let sum = 0;
        while (n) {
            sum += Math.pow(n % 10, 2);
            n = Math.floor(n/10);
        }
        n = sum;
    }
    return true;
};