Introduction:
Binary trees are fundamental data structures used in computer science and are a common topic in technical interviews. They offer a great way to explore various algorithms and data manipulation techniques. To help you prepare for your next interview, we’ve compiled a list of the top 50 binary tree questions from LeetCode, along with detailed explanations and solutions in simple language.
1. Question: Validate Binary Search Tree
- Problem: Given a binary tree, determine if it is a valid binary search tree.
- Solution: Perform an in-order traversal and check if the elements are in ascending order.
2. Question: Maximum Depth of Binary Tree
- Problem: Find the maximum depth of a binary tree.
- Solution: Recursively traverse the tree and keep track of the depth.
3. Question: Symmetric Tree
- Problem: Check if a binary tree is symmetric (mirrored).
- Solution: Compare the left and right subtrees of the root.
4. Question: Diameter of Binary Tree
- Problem: Find the length of the longest path between any two nodes in a binary tree.
- Solution: Calculate the depth of left and right subtrees and sum them.
5. Question: Lowest Common Ancestor of a Binary Tree
- Problem: Find the lowest common ancestor of two given nodes in a binary tree.
- Solution: Use a recursive approach to find the LCA.
6. Question: Binary Tree Level Order Traversal
- Problem: Return the level order traversal of a binary tree.
- Solution: Use a queue to perform level-order traversal.
7. Question: Serialize and Deserialize Binary Tree
- Problem: Serialize a binary tree into a string and deserialize it back to a tree.
- Solution: Use pre-order traversal for serialization and recursion for deserialization.
8. Question: Binary Tree Zigzag Level Order Traversal
- Problem: Return the zigzag (or spiral) level order traversal of a binary tree.
- Solution: Modify the level order traversal to alternate between left and right.
9. Question: Construct Binary Tree from Preorder and Inorder Traversal
- Problem: Build a binary tree from given preorder and inorder traversal arrays.
- Solution: Recursively divide the arrays to construct the tree.
10. Question: Path Sum
- Problem: Determine if there exists a path in a binary tree where the sum of the values equals a given target.
- Solution: Use depth-first search (DFS) to explore all paths.
11. Question: Flatten Binary Tree to Linked List
- Problem: Flatten a binary tree into a linked list in-place.
- Solution: Use a recursive approach to flatten the tree.
12. Question: Invert Binary Tree
- Problem: Invert a binary tree.
- Solution: Swap the left and right subtrees recursively.
13. Question: Binary Tree Right Side View
– Problem: Return the rightmost values at each level of a binary tree.
– Solution: Modify the level order traversal to return the rightmost values.
14. Question: Count Complete Tree Nodes
– Problem: Count the total number of nodes in a complete binary tree.
– Solution: Use binary search to find the last level and count the nodes.
15. Question: Subtree of Another Tree
– Problem: Check if one binary tree is a subtree of another.
– Solution: Use recursion to compare trees.
16. Question: Binary Tree Pruning
– Problem: Remove all subtrees containing only 0s.
– Solution: Use post-order traversal to prune the tree.
17. Question: Convert Sorted Array to Binary Search Tree
– Problem: Convert a sorted array into a height-balanced binary search tree.
– Solution: Recursively build the tree from the middle element.
18. Question: Populating Next Right Pointers in Each Node
– Problem: Populate each next pointer to point to its next right node.
– Solution: Use level-order traversal with a queue.
19. Question: Binary Tree Maximum Path Sum
– Problem: Find the maximum path sum in a binary tree.
– Solution: Use a recursive approach to calculate the maximum path sum.
20. Question: Convert Binary Search Tree to Sorted Doubly Linked List
– Problem: Convert a binary search tree into a doubly linked list in place.
– Solution: Perform in-order traversal while updating pointers.
21. Question: Unique Binary Search Trees
– Problem: Find the number of unique binary search trees that can be formed with ‘n’ nodes.
– Solution: Use dynamic programming to calculate the number of unique trees.
22. Question: Find Duplicate Subtrees
– Problem: Find all duplicate subtrees in a binary tree.
– Solution: Serialize subtrees and use a hash table to track duplicates.
23. Question: All Nodes Distance K in Binary Tree
– Problem: Find all nodes at distance ‘K’ from a given target node in a binary tree.
– Solution: Use depth-first search with backtracking to traverse the tree.
24. Question: Maximum Width of Binary Tree
– Problem: Find the maximum width of a binary tree.
– Solution: Use level-order traversal and maintain a list of indices.
25. Question: Binary Tree Cam
- Problem: Check if it is possible to make the binary tree a univalue tree by removing exactly one node.
- Solution: Use recursion to check the conditions.
26. Question: Maximum Binary Tree
– Problem: Construct a maximum binary tree from an input array.
– Solution: Find the maximum element, divide the array, and build the tree recursively.
27. Question: Recover Binary Search Tree
– Problem: Recover a binary search tree where two elements have been swapped.
– Solution: Use in-order traversal to identify and swap the misplaced elements.
28. Question: Find Elements in a Contaminated Binary Tree
– Problem: Implement a data structure that can recover the original binary tree.
– Solution: Use a hash set to keep track of visited nodes and recover the tree.
29. Question: Construct Binary Tree from Inorder and Postorder Traversal
– Problem: Build a binary tree from given inorder and postorder traversal arrays.
– Solution: Recursively divide the arrays to construct the tree.
30. Question: Delete Node in a BST
– Problem: Delete a node with a given value in a binary search tree.
– Solution: Recursively traverse the tree and update the links.
31. Question: Maximum Sum BST in Binary Tree
– Problem: Find the maximum sum binary search tree in a given binary tree.
– Solution: Use a recursive approach to check if a subtree is a valid BST.
32. Question: Merge Two Binary Trees
– Problem: Merge two binary trees by summing their values.
– Solution: Use a recursive approach to merge the trees.
33. Question: Binary Tree Vertical Order Traversal
– Problem: Return the vertical order traversal of a binary tree.
– Solution: Use a hash map to group nodes by their horizontal distance.
34. Question: Sum of Root To Leaf Binary Numbers
– Problem: Find the sum of all root-to-leaf binary numbers.
– Solution: Use a depth-first search approach and accumulate binary numbers.
35. Question: Find a Corresponding Node of a Binary Tree in a Clone of That Tree
– Problem: Given the cloned tree and a target node, find the corresponding node in the original tree.
– Solution: Traverse both trees in parallel and find the corresponding node.
36. Question: Binary Tree Coloring Game
– Problem: Determine if the first player can guarantee a win in a coloring game.
– Solution: Analyze the game by counting nodes in subtrees.
37. Question: Merge Trees
– Problem: Merge two binary trees by summing their values.
– Solution: Use a recursive approach to merge the trees.
38. Question: Binary Tree Tilt
– Problem: Find the tilt of a binary tree.
– Solution: Calculate the tilt of each node and sum them up.
39. Question: All Possible Full Binary Trees
– Problem: Generate all possible full binary trees with ‘N’ nodes.
– Solution: Use recursion to build trees with specific node counts.
40. Question: Delete Leaves With a Given Value
– Problem: Remove all leaf nodes with a given value from a binary tree.
– Solution: Use a recursive approach to prune the tree.
41. Question: Distribute Coins in Binary Tree
– Problem: Find the minimum number of moves to distribute coins in a binary tree.
– Solution: Use a depth-first search approach to balance the coins.
42. Question: Construct Binary Search Tree from Preorder Traversal
– Problem: Build a binary search tree from a preorder traversal array.
– Solution: Use a recursive approach to construct the tree.
43. Question: Leaf-Similar Trees
– Problem: Check if two binary trees have the same leaf value sequence.
– Solution: Use depth-first search to get leaf values and compare them.
44. Question: Cousins in Binary Tree
– Problem: Determine if two nodes are cousins in a binary tree.
– Solution: Use depth-first search to find depth and parent of nodes.
45. Question: Sum of Nodes with Even-Valued Grandparent
– Problem: Find the sum of nodes in a binary tree whose grandparent’s value is even.
– Solution: Use depth-first search to traverse the tree.
46. Question: Closest Leaf in a Binary Tree
– Problem: Find the closest leaf to a target node in a binary tree.
– Solution: Use depth-first search to find distances and traverse the tree.
47. Question: Binary Tree Longest Consecutive Sequence
– Problem: Find the longest consecutive sequence in a binary tree.
– Solution: Use depth-first search to track consecutive sequences.
48. Question: Minimum Depth of Binary Tree
– Problem: Find the minimum depth of a binary tree.
– Solution: Use depth-first search to track minimum depth.
49. Question: Find a Corresponding Node of a Binary Tree in a Clone of That Tree
– Problem: Given the cloned tree and a target node, find the corresponding node in the original tree.
– Solution: Traverse both trees in parallel and find the corresponding node.
50. Question: Maximum Width of Binary Tree
– Problem: Find the maximum width of a binary tree.
– Solution: Use level-order traversal and maintain a list of indices.
Conclusion:
Binary tree questions are a common part of technical interviews, and mastering them is crucial for success. This list of 50 binary tree questions and answers from Top 50 LeetCode Questions for Interview covers a wide range of topics and difficulty levels. By understanding these questions and practicing the provided solutions, you’ll be well-prepared to tackle binary tree-related interview questions with confidence. Remember to practice coding and analyzing binary tree problems regularly to excel in your interviews. Top 50 LeetCode Questions for Interview. Good luck!
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