202. Happy Number

Happy Number

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

Credits:Special thanks to @mithmatt and @ts for adding this problem and creating all test cases.

Solution

public class Solution {
  public boolean isHappy(int n) {
        Set<Integer> history = new HashSet<>();

        while (!history.contains(n)) {
            int tmp = calculate(n);
            history.add(n);

            if (tmp == 1) {
                return true;
            }

            n = tmp;
        }


        return false;
    }

    public int calculate(int n) {
        int result = 0;

        while (n != 0) {
            result += Math.pow(n % 10, 2);
            n /= 10;
        }

        return result;
    }

}