⚠️ This visualization was AI-generated and may contain inaccuracies. Please verify against the original LeetCode problem (#297) before relying on it.
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📦 Serialize and Deserialize Binary Tree

An interactive visualization of preorder DFS serialization and deserialization. Watch the tree convert to a string representation and back, node by node.

DFS LeetCode 297 ↗ Hard

The Problem

Design an algorithm to serialize and deserialize a binary tree. Serialization is the process of converting a tree to a string. Deserialization is reconstructing the tree from that string.

There is no restriction on how your serialization/deserialization algorithm should work — you just need to ensure that a binary tree can be serialized to a string and that this string can be deserialized back to the original tree structure.

Example: The tree [1,2,3,null,null,4,5] serializes to "1,2,null,null,3,4,null,null,5,null,null" using preorder DFS with null markers.

Interactive Visualization

Speed:
Binary Tree
Serialized String
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How It Works


        
Key Insight

        

            Preorder traversal (root, left, right) with null markers uniquely identifies a binary tree.
            By recording "null" for every missing child, we capture the full structure — not just the values.
            During deserialization, we consume tokens in the exact same preorder sequence, using "null" tokens
            to know when a subtree is empty and we should backtrack.
        


        
Serialize Algorithm

        
    
            
  • Perform a preorder DFS (visit root, then left subtree, then right subtree).
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  • At each node, append the node's value to the result list.
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  • When you reach a null child, append the string "null".
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  • Join all tokens with commas to produce the final string.
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Deserialize Algorithm

        
    
            
  • Split the serialized string by commas to get a list of tokens.
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  • Maintain a pointer i that tracks which token to consume next.
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  • Recursively build the tree in preorder: consume a token, create a node (or return null), then recurse for left and right children.
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  • The pointer ensures each token is consumed exactly once in the correct order.
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Complexity

        

            

                Time
                O(n)
            

            

                Space
                O(n)
            

        

        

            Both serialization and deserialization visit each node exactly once. The serialized string and
            the reconstructed tree each use O(n) space, where n is the number of nodes.
            The recursion stack uses O(h) space where h is the height of the tree (O(n) in the worst case for a skewed tree).