Added a file named 'digit_dp.cpp' that implements digit dynamic programming alogrithm in c++ language.

[vaibhavjain30699]

IMPORTANT: Please do not create a Pull Request without creating an issue first.

Any change needs to be discussed before proceeding.

Description

Please describe what changes you have made.

For Example:

• Added a file(s) named '...' that implements '...'.

• Changed the algorithm for performance/readablity/bugs.

• Added documentation to the algorithm

Related Issue

This project only accepts pull requests related to open issues.

If suggesting a new feature or change, please discuss it in an issue first.

If fixing a bug, there should be an issue describing it with steps to reproduce.

Please link to the issue here:

How Has This Been Tested? (Optional)

Please describe in detail how you tested your changes. You can skip this if you have not added any tests.

Screenshots (Optional)

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• [ ] Bug fix (change which fixes an issue with the algorithm)

• [ ] New Algorithm (non-breaking change which adds functionality)

• [ ] Documentation

Checklist:

Go over all the following points, and put an x in all the boxes that apply.

If you're unsure about any of these, don't hesitate to ask. We're here to help!

• [ ] My code follows the code style of this project.

• [ ] My change requires a change to the documentation.

• [ ] I have updated the documentation accordingly.

• [ ] I have read the CONTRIBUTING document.