LeetCode之旅（18）-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.

Example: 19 is a happy number

12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

思路

题目大意是要求将每个数字的平方相加，阵作为新的数字，一直计算下去，直到和为1，否则是会循环的。首先我把1~20的算了一下，发现没有总结出规律，不过不满足条件的数字是会循环出现，这样就可以判断如在等于一之前循环了，就不满足条件。（另外像这种平方的数字，不太好总结规律） 

代码

public class Solution {
     public int getHappy(int n){
        int sum =0;
        while(n!=0){
            sum += (n%10) * (n%10);
            n = n/10;
        }
        return sum;
    }
    public boolean isHappy(int n) {
        HashSet<Integer> happySet = new HashSet<Integer>();
        while(n!=1){
            if(happySet.contains(n))
                return false;
            happySet.add(n);
            n = getHappy(n);
        }
        return true;
    }
}