202. Happy Number

import java.util.HashSet;

/**
 * Created by clearbug on 2018/2/26.
 */
public class Solution {

    public static void main(String[] args) {
        Solution s = new Solution();
        System.out.println(s.isHappy(1));
        System.out.println(s.isHappy(2));
        System.out.println(s.isHappy(19));
    }

    /**
     * 方法一：这道题目没看出啥太大的规律性，只简单的发现只要 n % 10 == 0 时，那么便是返回 true 的时候了；同时为了防止无限循环，必须用
     * 一个数组来存储处理过的数值，若出现循环了则返回 false；
     *
     * @param n
     * @return
     */
    public boolean isHappy(int n) {
        HashSet<Integer> set = new HashSet<>();

        while (set.add(n)) {
            if (n == 1) {
                return true;
            }

            n = nextN(n);
        }

        return false;
    }

    private int nextN(int n) {
        int res = 0;
        while (n >= 10) {
            int remainder = n % 10;
            res += remainder * remainder;
            n /= 10;
        }
        if (n > 0) {
            res += n * n;
        }
        return res;
    }
}