【Leetcode】Happy Number

標籤：

題目連結：https://leetcode.com/problems/happy-number/

題目：

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

思路：

如果計算結果中出現4或它自身，則不是快樂數。

演算法：

[java] view plain copy 

1. public boolean isHappy(int n) {  
2.         char c[] = String.valueOf(n).toCharArray();  
3.         int sum = 0;  
4.         for (char t : c) {  
5.             int x = Integer.parseInt(String.valueOf(t));  
6.             sum += x * x;  
7.         }  
8.         if (sum == 1) {  
9.             return true;  
10.         } else if (sum == 4 || sum == n)  
11.             return false;  
12.         else if (isHappy(sum))  
13.             return true;  
14.         return false;  
15.     }  

【Leetcode】Happy Number