FAQs or Interview Questions on Data Structures

Here are some of the interview questions on data structures that are frequently asked in companies.
Hopefully this post might help some one to crack their interview

What is data structure?  

A data structure is a way of organizing data that considers not only the items stored, but also their relationship to each other.
Advance knowledge about the relationship between data items allows designing of efficient algorithms for the manipulation of data.

If you are using C language to implement the heterogeneous linked list, what pointer type will you use?

The heterogeneous linked list contains different data types in its nodes and we need a link, pointer to connect them. It is not possible to use ordinary pointers for this. So we go for void pointer. Void pointer is capable of storing pointer to any type as it is a generic pointer type.

Minimum number of queues needed to implement the priority queue?

Two. One queue is used for actual storing of data and another for storing priorities.

What is the data structure used to perform recursion?

Stack. Because of its LIFO (Last In First Out) property it remembers its ‘caller’ so knows whom to return when the function has to return. Recursion makes use of system stack for storing the return addresses of the function calls. Every recursive function has its equivalent iterative (non-recursive) function. Even when such equivalent iterative procedures are written, explicit stack is to be used.

What are the notations used in Evaluation of Arithmetic Expressions using prefix and postfix forms?

Polish and Reverse Polish notations.

Convert the expression ((A + B) * C – (D – E) ^ (F + G)) to equivalent Prefix and Postfix notations.
Prefix Notation:

^ - * +ABC - DE + FG

Postfix Notation:

AB + C * DE - - FG + ^

Sorting is not possible by using which of the following methods?
(a) Insertion (b) Selection (c) Exchange (d) Deletion

Answer: (d) Deletion.

Using insertion we can perform insertion sort, using selection we can perform selection sort, using exchange we can perform the bubble sort (and other similar sorting methods). But no sorting method can be done just using deletion.

A binary tree with 20 nodes has null branches?

21

Let us take a tree with 5 nodes (n=5)

A binary tree with n nodes has exactly n+1 null nodes.

How many different trees are possible with 10 nodes ?

1014
For example, consider a tree with 3 nodes(n=3), it will have the maximum combination of 5 different (ie, 23 - 3 = 5) trees.

If there are n nodes, there exist 2n-n different trees.

List out few of the Application of tree data-structure?

􀂾 The manipulation of Arithmetic expression,

􀂾 Symbol Table construction,

􀂾 Syntax analysis.

What is the type of the algorithm used in solving the 8 Queens problem?

Backtracking

In an AVL tree, at what condition the balancing is to be done?

If the ‘pivotal value’ (or the ‘Height factor’) is greater than 1 or less than –1.

What is the bucket size, when the overlapping and collision occur at same time?

One. If there is only one entry possible in the bucket, when the collision occurs, there is no way to accommodate the colliding value. This results in the overlapping of values.

There are 8, 15, 13, 14 nodes were there in 4 different trees. Which of them could have formed a full binary tree?

15.

In general:

There are 2n-1 nodes in a full binary tree.

By the method of elimination:

Full binary trees contain odd number of nodes. So there cannot be full binary trees with 8 or 14 nodes, so rejected. With 13 nodes you can form a complete binary tree but not a full binary tree. So the correct answer is 15.

Note:

Full and Complete binary trees are different. All full binary trees are complete binary trees but not vice versa.

What is a spanning Tree?

A spanning tree is a tree associated with a network. All the nodes of the graph appear on the tree once. A minimum spanning tree is a spanning tree organized so that the total edge weight between nodes is minimized.

Classify the Hashing Functions based on the various methods by which the key value is found.

􀂾 Direct method,

􀂾 Subtraction method,

􀂾 Modulo-Division method,

􀂾 Digit-Extraction method,

􀂾 Mid-Square method,

􀂾 Folding method,

􀂾 Pseudo-random method.

Of the following tree structure, which is, efficient considering space and time complexities?

(a) Incomplete Binary Tree

(b) Complete Binary Tree

(c) Full Binary Tree

(b) Complete Binary Tree.

By the method of elimination:

Full binary tree loses its nature when operations of insertions and deletions are done. For incomplete binary trees, extra storage is required and overhead of NULL node checking takes place. So complete binary tree is the better one since the property of complete binary tree is maintained even after operations like additions and deletions are done on it.