Add 13_Roman_To_Integer.cpp to cpp folder

[rudrakshtank]

Description

Problem: Convert a Roman numeral string into its corresponding integer value.

Approach:

1. Store Roman numeral values in an unordered_map.
2. Traverse the string from right to left.
3. If the current numeral’s value is greater than or equal to the previous numeral’s value, add it to the total; otherwise, subtract it.
4. Update the prev character each iteration.
5. Return the final computed value.

Time Complexity: O(N), where N is the length of the input string.
Space Complexity: O(1), since only a fixed-size hash map is used.

Have you made changes in README file ?

• Added problem & solution under correct topic.
• Specified Space & Time complexity.
• Specified difficulty level, tag & Note(if any).

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Please also note any relevant details for your test configuration.

• Test A
• Test B

Make sure all below guidelines are followed else PR will get Reject:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code so that it is easy to understand
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

[welcome]

I can tell this is your first pull request! Thank you I'm so honored. 🎉🎉🎉 I'll take a look at it ASAP!