Serialize & Deserialize Tree 30 XP Hard

Design an algorithm to serialize a binary tree to a string and deserialize it back. The format must capture the structure completely including null nodes.

Preorder traversal with null markers. Serialize: DFS, write value or 'N' for null. Deserialize: read values, recursively build tree.

💡 Pro tip: Understand this problem deeply — don't just memorize the code. Try explaining the approach out loud as if teaching a friend. If you can explain it simply, you truly understand it!