# 202. Happy Number

**<font color=red>难度: Easy</font>**

## 刷题内容

> 原题连接

* https://leetcode.com/problems/happy-number/

> 内容描述

```
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: 

Input: 19
Output: true
Explanation: 
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1
```

## 解题方案

> 思路 1
******- 时间复杂度: O(1)******- 空间复杂度: O(1)******

sb题没什么好说的, beats 98.71%

```python
class Solution:
    def isHappy(self, n):
        """
        :type n: int
        :rtype: bool
        """
        def squareSum(num):
            res = 0
            for i in str(num):
                res += int(i) ** 2
            return res
                
        lookup = set()
        happy_sum = squareSum(n)
        while happy_sum not in lookup and happy_sum != 1:
            lookup.add(happy_sum)
            happy_sum = squareSum(happy_sum)
        return True if happy_sum == 1 else False
```


可以看看这两篇post
1. [All you need to know about testing happy number!](https://leetcode.com/problems/happy-number/discuss/56918/All-you-need-to-know-about-testing-happy-number!)
2. [c++ using Floyd Cycle Detection Algorithm](https://leetcode.com/problems/happy-number/discuss/117136/c++-using-Floyd-Cycle-Detection-Algorithm)

会有一个更深的认知
