21 Binary Tree Interview Questions for Programmers

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Hello Devs, I have been sharing a lot of resources about programming job interviews like the books, courses, and some interview questions on the software design and data structures like an array, string, and linked list.

So far, we have looked at only the linear data structures, like an array and linked list, but all information in the real world cannot be represented in a linear fashion, and that's where tree data structure helps.

A tree data structure is a hierarchical data structure that allows you to store hierarchical data like a family tree or office hierarchy. Depending on how you store data, there are different types of trees, such as a binary tree, where each node has, at most, two child nodes.

Along with its close cousin binary search tree, it's also one of the most popular tree data structures.

Therefore, you will find a lot of questions based on them, such as how to traverse them, count nodes, find depth, and check if they are balanced or not.

A key point to solving binary tree questions is a strong knowledge of theory, like what is the size or depth of the binary tree, what is a leaf, and what is a node, as well as an understanding of the popular traversing algorithms, like pre-order, post-order, and in-order traversal.

If you are not familiar with these concepts then I strongly suggest you to first go through a comprehensive data structure and algorithm course likeData Structures and Algorithms: Deep Dive Using Java which explains essential data structure in detail.

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21 Best Binary Tree Interview Questions for Programmers

Now that you know how to solve binary tree-based coding problem using recursion and some tips about solving tree-based coding problems, here is a list of popular binary tree-based coding questions from software engineer or developer job interviews:

1. How is a binary search tree implemented? (solution)
2. How do you perform preorder traversal in a given binary tree? (solution)
3. How do you traverse a given binary tree in preorder without recursion? (solution)
4. How do you perform an inorder traversal in a given binary tree? (solution)
5. How do you print all nodes of a given binary tree using inorder traversal without recursion? (solution)
6. How do you implement a postorder traversal algorithm? (solution)

7. How do you traverse a binary tree in postorder traversal without recursion? (solution)
   For pre-order you need to first traverse root then left node and then right node.

8. How are all leaves of a binary search tree printed? (solution)

9. How do you count a number of leaf nodes in a given binary tree? (solution)

10. How do you perform a binary search in a given array? (solution)

11. How do you convert a given binary tree to double linked list in Java? (solution)

12. Write a program to find a depth of a given binary tree in Java? (solution)

13. What is the difference between binary and binary search trees? (answer)
    In Binary search tree, value of left node is less than or equal to root and value of right node is greater than or equal to root. In other words, all nodes in left sub tree are less than or equal to root and all nodes in right sub tree are greater than or equal to root of the tree.

14. What is a self-balanced tree? (answer)

15. What is the AVL Tree? (answer)
    AVL tree is a self balanced tree, precisely a height balanced binary search tree in which each node is associated with a balance factor which is calculated by subtracting the height of its right sub-tree from that of its left sub-tree.

16. You have given a BST, where two nodes are swapped? How do you recover the original BST? (solution)

17. How do you convert a binary tree to a binary search tree in Java? (solution)

18. Find the largest BST subtree of a given binary tree in Java? (solution)

19. Write a Java program to connect nodes at the same level as a binary tree? (solution)

20. What is a Trie data structure? (answer)

21. What is the difference between the Binary tree and Trie?
    Unlike a binary search tree, nodes in the trie do not store their associated key. Instead, a node's position in the trie defines the key with which it is associated. This distributes the value of each key across the data structure, and means that not every node necessarily has an associated value.

These are some of the most popular binary tree-based questions asked on Programming job interviews. You can solve them to become comfortable with tree-based problems.

If you feel that your understanding of binary tree coding is inadequate and you can't solve these questions on your own, I suggest you go back and pick a good data structure and algorithm courses like Easy to Advanced Data Structures by William Fiset, a former Google engineer, and former ACM-ICPC world finalist to refresh your knowledge about the binary tree and binary search tree.

If you need some more recommendations, here is my list of useful data structure algorithm books and courses to start with.

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Now You're One step closer to Crack your Programming interview

These are some of the most common questions about binary tree data structure form coding interviews that help you to do really well in your interview.

I have also shared a lot of data structure questions on my blog, so if you are really interested, you can always go there and search for them.

These common coding, data structure, and algorithm questions are the ones you need to know to successfully interview with any company, big or small, for any level of programming job.

If you are looking for a programming or software development job in 2022, you can start your preparation with this list of coding questions.

This list provides good topics to prepare and also helps assess your preparation to find out your areas of strength and weakness.

Good knowledge of data structure and algorithms is important for success in coding interviews and that's where you should focus most of your attention.

Resources

Here are my collection of best resources to prepare well for programming interviews in 2022.

1. Grokking the Coding Interview: Patterns for Coding Questions
2. Data Structures and Algorithms: Deep Dive Using Java
3. Data Structure and Algorithms Analysis --- Job Interview
4. Algorithms and Data Structure Part1 and 2
5. Data Structures in Java: An Interview Refresher
6. Grokking Dynamic Programming Patterns for Coding Interviews

Thanks for reading this far. Good luck with your programming interview! It's certainly not going to be easy, but by practicing these binary tree interview questions and using these resources, you are one step closer to cracking your next coding interview.

If you like this article, then please share it with your friends and colleagues, and don't forget to follow javinpaul on Twitter!

P.S. --- If you need more FREE resources to learn binary tree and other essential data structures, you can also check out this list of free data structure and algorithm courses to start your preparation.