## Description

https://leetcode.com/problems/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: **

Input:19Output:trueExplanation:1^{2}+ 9^{2}= 82 8^{2}+ 2^{2}= 68 6^{2}+ 8^{2}= 100 1^{2}+ 0^{2}+ 0^{2}= 1

## Explanation

Use a hashmap to check if the number gets a cycle.

## Python Solution

```
class Solution:
def isHappy(self, n: int) -> bool:
visited = {}
return self.is_happy_helper(n, visited)
def is_happy_helper(self, n, visited):
if n == 1:
return True
digits_sum = 0
while n != 0:
digit = n % 10
digits_sum += digit**2
n = n // 10
if digits_sum not in visited:
visited[digits_sum] = 1
else:
return False
return self.is_happy_helper(digits_sum, visited)
```

- Time complexity: O(n).
- Space complexity: O(n).

## 2 Thoughts to “LeetCode 202. Happy Number”