202. 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

public class Solution {
    public boolean isHappy(int n) {
        if(n<0) return false;
        List<Integer> nums = new ArrayList<>();
        nums.add(n);
        n = helper(n);
        while(n!=1){
            if(nums.contains(n)) return false;
            else nums.add(n);
            n = helper(n);
        }
        return true;
    }
    public int helper(int n){
        int result=0;
        while(n>0){
            result+=Math.pow(n%10,2);
            n/=10;
        }
        return result;
    }
}