Happy Number

题目
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.

答案

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