HappyNumber.js

/**
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
*/

/**
 * @param {number} n
 * @return {boolean}
 */
var isHappy = function(n) {
    let i = n, j = digitSquareSum(n);
    while (i !== j) {
        i = digitSquareSum(i);
        j = digitSquareSum(digitSquareSum(j));
    }
    return i === 1;
};
var digitSquareSum = function(n) {
    let temp = 0, sum = 0;
    while (n) {
        temp = n % 10;
        sum += temp * temp;
        n = parseInt(n / 10);
    }
    return sum;
}