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
Credits:
Special thanks to @mithmatt and @ts for adding this problem and creating all test cases.
思路：使用HashSet判断重复。
代码如下：
public class Solution {
public boolean isHappy(int n) {
if(n<1) return false;
if(n==1) return true;
Set<Integer>set=new HashSet<Integer>();
set.add(n);
while(true){
int m=0;
int sum=0;
while(n!=0){
m=n%10;
n=n/10;
sum+=m*m;
}
if(sum==1) return true;
if(set.contains(sum)) return false;
set.add(sum);
n=sum;
}
}
}
运行结果：
