202. Happy Number

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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

public class Solution {    public boolean isHappy(int n) {        HashSet<Integer> h=new HashSet<>();            int sum=0;            if(n==0)                return false;            if(n==1)                return true;            while(true)            {                while(n!=0)                {                    sum=sum+(n%10)*(n%10);                    n=n/10;                }                if(sum==1)                return true;                if(!h.add(sum))//如果set里面有重复的元素，说明进入死循环，add方法返回一个false                {                return false;                }                n=sum;                sum=0;            }    }}

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