Added Flatten Binary Tree algorithm in C++ under CPP/tree/

[PrakashShukla0907]

This pull request updates the Flatten Binary Tree implementation in C++ to allow users to build the binary tree dynamically from input instead of using a hardcoded structure.

Features

• Accepts user input to construct the binary tree recursively.
• Uses O(1) extra space (in-place modification).
• Prints inorder traversal of both the original and flattened trees.
• Clean and modular code with clear function separation:
  • buildTree() — builds the tree from input.
  • flatten() — flattens the binary tree.
  • inorder() — displays the inorder traversal.

Folder Structure

CPP/
└── tree/
└── flatten_binary_tree.cpp

[github-actions]

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[github-actions]

🤖 Automated PR Status

🔍 Code Validation

✅ Passed - File naming and structure look good!

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✅ Passed - All code compiles successfully!

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[admirerr]

Approved