Leetcode 12 - Integer to Roman

01-Jul-2026

Trying to solve these problems while also listening to a lecture might not be the most optimal, especially with how much time it took for me to finalize a solution for this question.

”To be an integer or not to be an integer, that is the question” - string

When approaching this question, I was stuck between converting num strings or to keep it as an integer. The idea behind it was by converting it to a container format, I can use the index as the digit count and not have to worry about tracking the digits. But with that setup, things didn’t work as well as I had hoped and the logic for dealing with exceptions, such as $4$ and $9$, was another thing that annoyed me.

With that, the approach was to keep the num as an integer, but crawl from the biggest value to the smallest, covering all the roman numerals. That means also including the exceptions as vector entries instead of having them as standalone logic checks. What this means is I can just go incrementally take away from num until it hits $0$, and return whatever combination of the roman numerals it collected.

After solving this, instead of using a map container, I could have just used a vector<pair<int,string>> instead to reduce the complexity of the data structure.

Performance evaluation

The time complexity of this solution is $O(n)$ since we have a fixed number of integer-roman pairs and we loop until num is back to zero. As for space, we’ve only used on additional variable so $O(1)$.

Hmmm… Are strings in C++ constant size? I remember reading that strings are also container components, meaning they act similar to vectors.

There was an attempt, but not a successful one

This is a failed attempt of mine, but what ultimately helped me clear my mind in finding the most appropriate solution for this problem.