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

 

题目很简单，关键在于终止条件的判断。

使用hashset，把每次需要被判断的n放进去，当有重复的值出现的时候说明会陷入死循环，终止，返回false即可。

 

 

参考代码：

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