added catalan number in cpp in dynamic programming

[RitikTiwary519]

Description

This PR adds the implementation of the Catalan Number algorithm using Dynamic Programming in C++ under the dynamic_programming directory.

Features:

• Efficient Bottom-Up DP approach.
• Time complexity reduced from exponential to O(n²).
• Includes inline comments and example usage in main() for quick testing.

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Time and Space Complexity

• Time Complexity: O(n^2)
• Space Complexity: O(n) (only stores the last n values)

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Files Added

catalan_number.cpp

Related Issue

No specific issue linked, but this adds a key combinatorial algorithm often used in competitive programming and dynamic programming problem sets.

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Sample Output

For n = 5, output will be: