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Serialize and Deserialize Binary Tree

HardAcceptance: 52.6%
Binary TreeTreeDesignStringDFSBFS

Problem Statement

Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to be reconstructed later in the same or another computer environment. Design an algorithm to serialize and deserialize a binary tree. 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 this string can be deserialized to the original tree structure.

Constraints:

  • The number of nodes in the tree is in the range [0, 10^4]
  • -1000 <= Node.val <= 1000
  • The input tree is guaranteed to be a binary tree

Input Format:

  • For serialize: A root node of a binary tree
  • For deserialize: A string representation of a binary tree

Output Format:

  • For serialize: A string representation of the binary tree
  • For deserialize: The reconstructed binary tree

Examples:

Example 1:

Input:

root = [1,2,3,null,null,4,5]

Output:

The binary tree should be recovered exactly as it was

Explanation:

The serialized string could be something like "1,2,3,null,null,4,5", which would deserialize back to the original binary tree with root = 1, left child = 2, right child = 3, and children 4 and 5 of node 3.

Example 2:

Input:

root = []

Output:

The empty binary tree should be recovered

Explanation:

An empty tree could be serialized as an empty string or a special marker, and should deserialize back to an empty tree.

Example 3:

Input:

root = [1,null,2,null,3,null,4,null,5]

Output:

The right-skewed binary tree should be recovered exactly as it was

Explanation:

A right-skewed tree where each node has only a right child should be serialized and deserialized correctly.

Solutions

Preorder DFS with Null Markers

Time: O(n) for both serialize and deserialize, where n is the number of nodes in the tree
Space: O(n) for both operations due to recursion and storage of the serialized string

Serialize the tree using preorder traversal (root-left-right), representing null pointers with a special marker. Deserialize by recursively reconstructing the tree following the same preorder sequence.

Level Order (BFS) Approach

Time: O(n) for both serialize and deserialize, where n is the number of nodes in the tree
Space: O(n) for both operations for storing the queue and the serialized string

Serialize the tree using level-order traversal (breadth-first), representing null pointers with a special marker. Deserialize by reconstructing the tree level by level.

Algorithm Walkthrough

Example input: nums = []

Step-by-step execution:

  1. For serialization with preorder DFS:
  2. Start traversal at the root node (1)
  3. Process root value: 1
  4. Recursively process left subtree (2) - add 2 to result
  5. Recursively process left's left subtree (null) - add 'X' to result
  6. Recursively process left's right subtree (null) - add 'X' to result
  7. Recursively process right subtree (3) - add 3 to result
  8. Recursively process right's left subtree (4) - add 4 to result
  9. Recursively process right's left's children - add 'X','X' to result
  10. Recursively process right's right subtree (5) - add 5 to result
  11. Recursively process right's right's children - add 'X','X' to result
  12. Result: '1,2,X,X,3,4,X,X,5,X,X'
  14. For deserialization:
  15. Parse the serialized string into values: [1,2,X,X,3,4,X,X,5,X,X]
  16. Read 1: Create root node with value 1
  17. Read 2: Create left child of node 1 with value 2
  18. Read X, X: Set both children of node 2 to null
  19. Read 3: Create right child of node 1 with value 3
  20. Read 4: Create left child of node 3 with value 4
  21. Read X, X: Set both children of node 4 to null
  22. Read 5: Create right child of node 3 with value 5
  23. Read X, X: Set both children of node 5 to null
  24. Final tree structure matches the original tree: [1,2,3,null,null,4,5]

Hints

Hint 1
Consider using a traversal method (preorder, inorder, level-order) to serialize the tree.
Hint 2
You need a way to represent null pointers in your serialized string.
Hint 3
For deserialization, you need to reconstruct the tree by following the same traversal pattern used during serialization.
Hint 4
For level-order traversal (BFS), consider using a queue to help with tree reconstruction.
Hint 5
For depth-first approaches, consider using recursion to handle the tree structure.

Video Tutorial

Serialize and Deserialize Binary Tree - DFS and BFS Approaches

YouTube•Learn the Serialize and Deserialize Binary Tree solution step-by-step

Video tutorials can be a great way to understand algorithms visually

Visualization

Visualize the tree structure and the serialization/deserialization process, showing how each node is processed during traversal.

Key visualization elements:

  • current node
  • serialized string
  • deserialized tree

Similar Questions

Construct Binary Tree from Preorder and Inorder Traversal

Medium

Given two integer arrays preorder and inorder where preorder is the preorder traversal of a binary tree and inorder is the inorder traversal of the same tree, construct and return the binary tree.

Encode and Decode Strings

Medium

Design an algorithm to encode a list of strings to a single string. The encoded string is then decoded back to the original list of strings. Implement the encode and decode methods.

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Implementation Notes

This problem is a fundamental one for understanding tree traversal and reconstruction algorithms. The preorder DFS approach is very intuitive for recursive structures like trees, but the BFS approach can also be effective and may produce a more compact representation for certain types of trees.