## Question

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*.

## Algorithm

Nothing special, you follow the requirement and implement it.

Use a set to store the sums to check if there are infinite loop. If so, return false; otherwise continue calculate the sums until sum = 1.

## Code

class Solution { public boolean isHappy(int n) { Set<Integer> set = new HashSet<>(); int num = calculateSum(n); while (num != 1) { if (!set.add(num)) { return false; } else { set.add(num); num = calculateSum(num); } } return true; } private int calculateSum(int n) { int sum = 0; while (n > 0) { int num = n % 10; sum += num * num; n /= 10; } return sum; } }