Algorithm Puzzles ~~everyday~~ ~~every week~~ sometimes: Add two numbers

## Puzzle

Puzzle from leetcode:

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)

Output: 7 -> 0 -> 8

Explanation: 342 + 465 = 807.

The template code provided by leetcode:

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## Solving

My first came out solution just like how we do sum on draft paper:

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Time complexity: O(n)

It’s do a little optimization:

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Super! Better than 99.99%!