20. Serialize Tree

PRO

Hard

Topics

Helpful tools to learn & understand

Visualize LogicActive Simulator

Watch key transitions, pointers, and variables update step-by-step.

Open

Check Solutions

Read clean, documented implementations across multiple patterns.

View Code

Thinkpad (Draw & Note)

Sketch diagrams on an infinite canvas and draft notes directly inline.

Draw

Example 1:

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

Output: [1,2,3,null,null,4,5]

Explanation: The input tree is serialized and then deserialized, resulting in the same tree structure.

Example 2:

Input: root = []

Output: []

Explanation: An empty tree is serialized to an empty string, which is then deserialized back into an empty tree.

Example 3:

Input: root = [1]

Output: [1]

Explanation: A single-node tree is serialized and deserialized correctly.

Serialize: use preorder traversal (root, left, right) with 'null' markers for empty nodes. Deserialize: reconstruct using the same preorder sequence by consuming values from queue/iterator.

Time Complexity

O(n)

Space Complexity