Happy Number

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

题目的关键是一直不等于1循环什么时候终止？终止的条件是number在以前的计算

中出现过，这样就没有再计算的必要了。

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

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