Problem

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

1^2 + 9^2 = 828^2 + 2^2 = 686^2 + 8^2 = 1001^2 + 0^2 + 0^2 = 1

Solution

updated 2018-9

class Solution {    public boolean isHappy(int n) {        Set
    
      record = new HashSet<>();        while (n != 1) {            if (record.contains(n)) return false;            record.add(n);            int sum = 0;            while (n != 0) {                //calculate sum                sum += Math.pow(n%10, 2);                n /= 10;            }            n = sum;        }        return true;    }}