leetcode -- happy number 快樂數

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

方法解析：

顯然，set集合適合於判斷各個數位的平方和是否重複，若已存在則false。

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