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53 worked problems

Binary Trees

Recursive structure — visit, go left, go right. Each answer can be composed from a node and the answers of its child subtrees.

Recognition signal

When should you think of Binary Trees?

Each answer can be composed from a node and the answers of its child subtrees.

Core invariant

What must stay true?

A traversal enters each node with a clear contract for what it returns or records.

Practice in a deliberate order

Starter

Build the template

  1. #94 Binary Tree Inorder TraversalEasy
  2. #100 Same TreeEasy
  3. #101 Symmetric TreeEasy
  4. #104 Maximum Depth of Binary TreeEasy
Core

Recognize variations

  1. #98 Validate Binary Search TreeMedium
  2. #102 Binary Tree Level Order TraversalMedium
  3. #103 Zigzag Level Order TraversalMedium
  4. #105 Construct BT from Preorder and InorderMedium
  5. #106 Construct BT from Postorder and InorderMedium
  6. #109 Convert Sorted List to BSTMedium
Stretch

Combine ideas under pressure

  1. #124 Binary Tree Maximum Path SumHard
  2. #173 BST IteratorHard
  3. #297 Serialize and Deserialize Binary TreeHard
  4. #545 Boundary of Binary TreeHard

What to learn in this cluster

  1. 01DFS and BFS traversal
  2. 02Path and ancestor reasoning
  3. 03BST invariants and tree construction

All Binary Trees problems

53 of 53 walkthroughs
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