Serialize and Deserialize Binary Tree
Problem Statement
Design a way to turn a binary tree into a string, and back into the same tree.
Write a Codec class with two methods. serialize takes the root and returns a string. deserialize takes that string and returns the root of a tree with the same shape and the same values. You choose the format. Any format works, as long as the round trip gives back the same tree.
For serialize: the root of a binary tree, which can be empty. For deserialize: a string made by serialize.
For serialize: a string. For deserialize: the root of the rebuilt tree.
The string can look like anything. What matters is that reading it back gives the same tree.
An empty tree must also survive the round trip.
- • 0 ≤ number of nodes ≤ 10^4
- • −1000 ≤ Node.val ≤ 1000
Pattern Recognition Clues
Recognising these key signals in the problem description immediately identifies the pattern:
Approach Complexity Ladder
Write the tree level by level with null for each missing child, and rebuild it with a queue
Write the tree in preorder with # for each missing child; read the tokens back in the same order
Write the tree the way LeetCode prints it: level by level, with null for every missing child. Read it back with a queue: the next two tokens are the children of the node at the front of the queue. The null entries keep the shape, so the writer and the reader match each other step for step.
Recognition rule for this sub-pattern:
Unlock Complete Visual Walkthrough & Optimal C++
The interactive animated dry-run player, optimized C++ implementation, state invariant derivations, and edge-case breakdown for this question are part of Brute2Best Pro. The anchor question of every sub-pattern is completely free.
First anchor question per pattern, Part 1 LLD & Module 1 C++ basics are 100% Free forever.
How this concept connects to System Design & C++ Systems
Top engineering interviews test whether you understand how algorithms like Tree DFS translate into production architectures and low-level memory mechanics.
Foundations: Object-Oriented Principles in C++23
Class invariants, pure virtual interfaces, and RAII smart pointers.
Food Delivery System (Zomato Architecture)
Real-world machine coding application of algorithms and design patterns.
Pointers vs References Deep Dive
Pointer arithmetic and memory layout under the hood.
Virtual Method Table (vtable) & Memory Layout
Polymorphism, vptr overhead, and multiple inheritance in memory.