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Master Binary Trees - Complete Pattern Guide for Interviews

· 9 min read

Trees show up in almost every technical interview. Not because interviewers are obsessed with them, but because tree problems reveal how you think recursively, manage state, and break down complex problems into simpler ones.

Pattern 1: Tree Traversal Basics​

Why This Pattern Matters: If you can't traverse a tree confidently, everything else falls apart. These are the building blocks. You should be able to write these in your sleep literally.

Practice Problems:

  1. Binary Tree Inorder Traversal
  2. Binary Tree Preorder Traversal
  3. Binary Tree Postorder Traversal
  4. Binary Tree Level Order Traversal
  5. Binary Tree Zigzag Level Order Traversal
  6. Binary Tree Vertical Order Traversal
  7. Binary Tree Right Side View

Pattern 2: Tree Properties & Measurements​

Why This Pattern Matters: These problems teach you to think about what information flows up from child nodes to parent nodes. This bottom-up thinking is crucial for harder problems.

Practice Problems:

  1. Maximum Depth of Binary Tree
  2. Minimum Depth of Binary Tree
  3. Diameter of Binary Tree
  4. Balanced Binary Tree
  5. Symmetric Tree
  6. Same Tree
  7. Subtree of Another Tree
  8. Count Complete Tree Nodes

Pattern 3: Path Problems​

Why This Pattern Matters: Path problems are EVERYWHERE in interviews. They test your ability to track state as you traverse and backtrack properly. This is where most candidates struggle.

Practice Problems:

  1. Path Sum
  2. Path Sum II
  3. Path Sum III
  4. Binary Tree Maximum Path Sum
  5. Sum Root to Leaf Numbers
  6. Binary Tree Paths
  7. Smallest String Starting From Leaf
  8. Longest Univalue Path

Pattern 4: Tree Construction & Modification​

Why This Pattern Matters: These problems test your understanding of tree structure at a deeper level. Can you build a tree from traversals? Can you modify tree structure correctly?

Practice Problems:

  1. Invert Binary Tree
  2. Construct Binary Tree from Preorder and Inorder Traversal
  3. Construct Binary Tree from Inorder and Postorder Traversal
  4. Maximum Binary Tree
  5. Flatten Binary Tree to Linked List
  6. Convert Sorted Array to Binary Search Tree
  7. Convert Sorted List to Binary Search Tree

Pattern 5: Binary Search Tree (BST) Specific​

Why This Pattern Matters: BSTs have special properties (left < root < right) that enable efficient operations. These problems test if you can exploit this property.

Practice Problems:

  1. Validate Binary Search Tree
  2. Kth Smallest Element in a BST
  3. Lowest Common Ancestor of a Binary Search Tree
  4. Convert BST to Greater Tree
  5. Delete Node in a BST
  6. Insert into a Binary Search Tree
  7. Recover Binary Search Tree
  8. Unique Binary Search Trees
  9. Unique Binary Search Trees II

Pattern 6: Lowest Common Ancestor (LCA)​

Why This Pattern Matters: LCA problems are a favorite interview topic because they test your ability to think about tree structure and information flow. The pattern appears in many disguised forms.

Practice Problems:

  1. Lowest Common Ancestor of a Binary Tree
  2. Lowest Common Ancestor of a Binary Search Tree
  3. Lowest Common Ancestor of Deepest Leaves
  4. Lowest Common Ancestor of a Binary Tree II
  5. Lowest Common Ancestor of a Binary Tree III
  6. Lowest Common Ancestor of a Binary Tree IV

Pattern 7: Views & Boundaries​

Why This Pattern Matters: These problems test your spatial reasoning with trees. Can you think about what's visible from different perspectives?

Practice Problems:

  1. Binary Tree Right Side View
  2. Boundary of Binary Tree
  3. Vertical Order Traversal of a Binary Tree
  4. Binary Tree Top View (Premium)
  5. Binary Tree Bottom View (Premium)

Pattern 8: Serialization & Deserialization​

Why This Pattern Matters: These problems test your understanding of tree structure and encoding schemes. Common in system design discussions too (how to store trees in databases).

Practice Problems:

  1. Serialize and Deserialize Binary Tree
  2. Serialize and Deserialize BST
  3. Encode N-ary Tree to Binary Tree
  4. Verify Preorder Serialization of a Binary Tree

Pattern 9: Tree DP & Optimization​

Why This Pattern Matters: These are the hardest tree problems. They combine tree traversal with dynamic programming thinking. Master these, and you're in the top tier.

Practice Problems:

  1. House Robber III
  2. Binary Tree Cameras
  3. Distribute Coins in Binary Tree
  4. Maximum Sum BST in Binary Tree
  5. Binary Tree Maximum Product of Splitted Tree
  6. All Possible Full Binary Trees

Pattern 10: N-ary Trees & Tries​

Why This Pattern Matters: Not all trees are binary. These problems test if you can generalize your tree thinking beyond the binary tree structure.

Practice Problems:

  1. Maximum Depth of N-ary Tree
  2. N-ary Tree Level Order Traversal
  3. N-ary Tree Preorder Traversal
  4. N-ary Tree Postorder Traversal
  5. Implement Trie (Prefix Tree)
  6. Word Search II
  7. Design Add and Search Words Data Structure
  8. Replace Words

Pattern 11: Ancestor & Parent Pointer Problems​

Why This Pattern Matters: Some tree problems give you parent pointers or ask you to track ancestors. These require different traversal strategies than standard tree recursion.

Practice Problems:

  1. Delete Nodes And Return Forest
  2. Find Distance in Binary Tree (Premium)
  3. Step-By-Step Directions From a Binary Tree Node to Another
  4. Closest Leaf in a Binary Tree (Premium)
  5. All Nodes Distance K in Binary Tree

Pattern 12: Hard Interview Favorites​

Why This Pattern Matters: These are the problems that show up in actual FAANG interviews most frequently, according to interview reports. Master these, and you're golden.

Practice Problems:

  1. Binary Tree Maximum Path Sum
  2. Serialize and Deserialize Binary Tree
  3. Lowest Common Ancestor of a Binary Tree
  4. Validate Binary Search Tree
  5. Construct Binary Tree from Preorder and Inorder Traversal
  6. Kth Smallest Element in a BST
  7. Count Complete Tree Nodes
  8. Binary Tree Cameras
  9. Word Search II
  10. Recover Binary Search Tree

Happy coding! 🚀