Tree Data Structure Questions for Coding Interviews Preparation

Hello folks, 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 first go through a comprehensive data structure and algorithm course which explains essential data structure in detail.

Binary Tree Based Coding Problems for Interviews

Now that you know how to solve binary tree-based coding problems 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. What is the difference between binary and binary search trees? (Answer)
   A Binary Tree is a basic structure with a simple rule that no parent must have more than 2 children whereas the Binary Search Tree is a variant of the binary tree following a particular order with which the nodes should be organized. In a binary search tree, values of nodes on the left subtree are less than or equal to root, and values of nods on the right subtrees are greater than or equal to root.

2. What is a self-balanced tree? (Answer)
   Self-Balancing Binary Search Trees are height-balanced binary search trees that automatically keep the height as small as possible when insertion or deletion happens. Hence, for self-balancing BSTs, the minimum height must always be log₂(n) rounded down. In another word, A tree is balanced if, for every node in the tree, the height of its right and left subtrees differs by at most 1

3. What is the AVL Tree? (Answer)
   An AVL tree is a self-balancing binary search tree. It was the first such data structure to be invented. In an AVL tree, the heights of the two-child subtrees of any node differ by at most one; if at any time they differ by more than one, rebalancing is done to restore this property

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?
   You can use stack to replace recursion as given in the solution (Solution)

6. How do you implement a postorder traversal algorithm? (Solution)
   Postorder means LRN (left tree, right tree, node), which means the root is visited last

7. How are all leaves of a binary search tree printed? (Answer)
   Here are the steps you can follow to print all leaf nodes of a binary tree:

   1. If give tree node or root is null then return.
   2. Print the node if both right and left tree is null, that's your leaf node.
   3. Repeat the process with both left and right subtrees.

8. How do you count the number of leaf nodes in a given binary tree? (Answer)

   Here is an iterative algorithm to get the total number of leaf nodes of the binary tree:

   1.  If the root is null then return zero.
   2.  Start the count with zero.
   3.  Push the root into Stack.
   4.  Loop until Stack is not empty.
   5.  Pop the last node and push the left and right children of the last node if they are not null.

9. How is a binary search tree implemented? (solution)
   A Binary tree is implemented with the help of objects. The first node in the tree is represented by the root object. Each node in the tree consists of three parts, i.e., data, left node, and right node. To create a binary tree, we first need to create the node or TreeNode object like this:

   Java

    

   class TreeNode{
     TreeNode right;
     TreeNode left;
     int data;
   }

   
   

10. How do you traverse a given binary tree in preorder without recursion? (Solution)
    Pre-order traversal in Java without recursion

    1. Create an empty stack.
    2. Push the root into Stack.
    3. Loop until Stack is empty.
    4. Pop the last node and print its value.
    5. Push right and left nodes if they are not null.
    6. Repeat from steps 4 to 6 again.

11. What is a Trie data structure? (Answer)
    A trie is an ordered data structure, a type of search tree used to store associative data structures. It is also referred to as a Radix tree or Prefix tree.

12. What is the difference between the Binary tree and Trie? (Answer)
    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 in 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 course to refresh your knowledge about the binary tree and binary search tree.

Now You're One Step Closer to the Coding Interview

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

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 2021, 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.

Conclusion

Thanks, you made it to the end of the article. Good luck with your programming interview! It's certainly not going to be easy, but by following this roadmap and guide, you are one step closer to becoming a Software Developer.

P.S. --- If you need some FREE resources, you can check out this list of free data structure and algorithm courses to start your preparation.