Happy Number

lc 202

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.

所有数字每一个加起来的结果重复进行计算，直到结果变成1或者结果循环为止。

我一开始的做法优点笨，把正数转成了string，然后一位一位的算，这样new了好几个string，其实对于一个整数，利用除以10，余数就是最末尾的数，然后再除10，商就是下一位的数。。思路比较好。

public class Solution {
    private int getNextHappy(int n) {
        int sum = 0;
        while (n != 0) {
            sum += (n % 10) * (n % 10);
            n /= 10;
        }
        return sum;
    }

    public boolean isHappy(int n) {
        HashSet<Integer> hash = new HashSet<Integer>();
        while (n != 1) {
            if (hash.contains(n)) {
                return false;
            }
            hash.add(n);
            n = getNextHappy(n);
        }
        return true;
    }
}