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

1^2 + 9^2 = 82
8^2 + 2^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 0^2 = 1

Will this method ever terminate? yes, the number square sum will not increase for ever. if you get the maximum 3-digit number, 999, 3*9^2 = 243, so the number will go up, then go down.

public class Solution {
    public boolean isHappy(int n) {
        Set<Integer> set = new HashSet<>();
        while(true){
            if(n == 1 ) return true;

            if(set.contains(n)){
                return false;
            }else{
                set.add(n);
            }
            int res =0;
            while(n > 0){
                res += (n%10) * (n%10);
                n /= 10;
            }
            n = res;
        }
    }
}