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;
}
}