# Contest - Day 2 - Happy Number

Leetcode is running a 30 day “Covid 19” style contest for everyone on self quarantine and social distancing. Let’s jump in!

## Happy Number

### Problem

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
```

### Thinking

Once you know how to pull individual digits out of a number, these are *relatively* straight forward. You just need to keep track of your in-progress sums vs. total sums and the total sums you’ve previously seen for loop detection.

To get a digit, you just mod the number by its base (`10`

, assuming its `base 10`

). Then you divide the original number by its base and continue. An unrolled look for the number `19`

would look like:

### Corner Cases

I don’t think I missed any this time.

### Improvements

There’s possibly a way to detect loops without using a set (mathematical) to decrease memory usage but I don’t know of it.

### Solution

### Score

```
Runtime: 36 ms, faster than 30.40% of Python3 online submissions for Happy Number.
Memory Usage: 13.9 MB, less than 5.26% of Python3 online submissions for Happy Number.
```