Data structures

Dr.Maya Nayak
Data Structures:
Questions and Answers
By
Dr.Maya Nayak
1. 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.
 Data structure refers to the way data is organized and manipulated. It
seeks to find ways to make data access more efficient. When dealing
with the data structure, we not only focus on one piece of data but the
different set of data and how they can relate to one another in an
organized manner.
2. List out the areas in which data structures are applied extensively?
 Compiler Design
 Operating System
 Database Management System
 Statistical analysis package
 Numerical Analysis
 Graphics
 Artificial Intelligence
 Simulation
3. What are the major data structures used in the following areas : RDBMS,
Network data model and Hierarchical data model.
 RDBMS = Array (i.e. Array of structures)
 Network data model = Graph
 Hierarchical data model = Trees
4. If you are using C language to implement the heterogeneous linked list, what
pointer type will you use?

Dr.Maya Nayak
 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.
5. 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.
6. What is the data structures 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.
7. 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.
8. In tree construction which is the suitable efficient data structure? (Array,
Linked list, Stack, Queue)
 Linked list is the suitable efficient data structure.
9. What is the type of the algorithm used in solving the 8 Queens problem?
 Backtracking.
10. 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.
11. 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.
12. Classify the Hashing Functions based on the various methods by which the
key value is found.

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 Direct method
 Subtraction method
 Modulo-Division method
 Digit-Extraction method
 Mid-Square method
 Folding method
 Pseudo-random method
13. What are the types of Collision Resolution Techniques and the methods
used in each of the type?
 Open addressing (closed hashing), The methods used include:
Overflow block.
 Closed addressing (open hashing), The methods used include: Linked
list, Binary tree.
14. In RDBMS, what is the efficient data structure used in the internal storage
representation?
 B+ tree. Because in B+ tree, all the data is stored only in leaf nodes,
that makes searching easier. This corresponds to the records that shall
be stored in leaf nodes.
15. 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.
16. Does the minimum spanning tree of a graph give the shortest distance
between any 2 specified nodes?
 No. The Minimal spanning tree assures that the total weight of the
tree is kept at its minimum. But it doesn't mean that the distance
between any two nodes involved in the minimum-spanning tree is
minimum.
17. Which is the simplest file structure? (Sequential, Indexed, Random)
 Sequential is the simplest file structure.
18. Whether Linked List is linear or Non-linear data structure?
 According to Access strategies Linked list is a linear one.
 According to Storage Linked List is a Non-linear one.

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19. Differentiate between file and structure storage structure.
 The key difference between both the data structure is the memory
area that is being accessed. When dealing with the structure that
resides the main memory of the computer system, this is referred to
as storage structure. When dealing with an auxiliary structure, we
refer to it as file structures.
20. When is a binary search best applied?
 A binary search is an algorithm that is best applied to search a list
when the elements are already in order or sorted. The list is searched
starting in the middle, such that if that middle value is not the target
search key, it will check to see if it will continue the search on the
lower half of the list or the higher half. The split and search will then
continue in the same manner.
21. What is a linked list?
 A linked list is a sequence of nodes in which each node is connected
to the node following it. This forms a chain-like link for data storage.
22. How do you reference all the elements in a one-dimension array?
 To reference all the elements in a one -dimension array, you need to
use an indexed loop, So that, the counter runs from 0 to the array size
minus one. In this manner, You can reference all the elements in
sequence by using the loop counter as the array subscript.
23. In what areas do data structures are applied?
 Data structures are essential in almost every aspect where data is
involved. In general, algorithms that involve efficient data structure is
applied in the following areas: numerical analysis, operating system,
A.I., compiler design, database management, graphics, and statistical
analysis, to name a few.
24. What is LIFO?

Dr.Maya Nayak
 LIFO is a short form of Last In First Out. It refers how data is
accessed, stored and retrieved. Using this scheme, data that was
stored last should be the one to be extracted first. This also means
that in order to gain access to the first data, all the other data that was
stored before this first data must first be retrieved and extracted.
25. What is a queue?
 A queue is a data structure that can simulate a list or stream of data.
In this structure, new elements are inserted at one end, and existing
elements are removed from the other end.
26.What are binary trees?
 A binary tree is one type of data structure that has two nodes, a left
node, and a right node. In programming, binary trees are an extension
of the linked list structures.
27. Which data structures are applied when dealing with a recursive function?
 Recursion, is a function that calls itself based on a terminating
condition, makes use of the stack. Using LIFO, a call to a recursive
function saves the return address so that it knows how to return to the
calling function after the call terminates.
28. What is a stack?
 A stack is a data structure in which only the top element can be
accessed. As data is stored in the stack, each data is pushed
downward, leaving the most recently added data on top.
29. Explain Binary Search Tree?
 A binary search tree stores data in such a way that they can be
retrieved very efficiently. The left subtree contains nodes whose keys
are less than the node’s key value, while the right subtree contains
nodes whose keys are greater than or equal to the node’s key value.
Moreover, both subtrees are also binary search trees.
30. What are multidimensional arrays?
 Multidimensional arrays make use of multiple indexes to store data.
It is useful when storing data that cannot be represented using single
dimensional indexing, such as data representation in a board game,
tables with data stored in more than one column.
31. Are linked lists considered linear or non-linear data structures?

Dr.Maya Nayak
 It depends on where you intend to apply linked lists. If you based it
on storage, a linked list is considered non-linear. On the other hand,
if you based it on access strategies, then a linked list is considered
linear.
32. How does dynamic memory allocation help in managing data?
 Apart from being able to store simple structured data types, dynamic
memory allocation can combine separately allocated structured
blocks to form composite structures that expand and contract as
needed.
33. What is FIFO?
 FIFO stands for First-in, First-out, and is used to represent how data
is accessed in a queue. Data has been inserted into the queue list the
longest is the one that is removed first.
34. What is an ordered list?
 An ordered list is a list in which each node’s position in the list is
determined by the value of its key component, so that the key values
form an increasing sequence, as the list is traversed.
35. What is merge sort?
 Merge sort, is a divide-and-conquer approach for sorting the data. In
a sequence of data, adjacent ones are merged and sorted to create
bigger sorted lists. These sorted lists are then merged again to form
an even bigger sorted list, which continues until you have one single
sorted list.
36.Differentiate NULL and VOID?
 Null is a value, whereas Void is a data type identifier. A variable that
is given a Null value indicates an empty value. The void is used to
identify pointers as having no initial size.
37.What is the primary advantage of a linked list?
 A linked list is an ideal data structure because it can be modified
easily. This means that editing a linked list works regardless of how
many elements are in the list.
38. What is the difference between a PUSH and a POP?
 Pushing and popping applies to the way data is stored and retrieved
in a stack. A push denotes data being added to it, meaning data is

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being “pushed” into the stack. On the other hand, a pop denotes data
retrieval, and in particular, refers to the topmost data being accessed.
37.What is a linear search?
 A linear search refers to the way a target key is being searched in a
sequential data structure. In this method, each element in the list is
checked and compared against the target key. The process is repeated
until found or if the end of the file has been reached.
38. How does variable declaration affect memory allocation?
 The amount of memory to be allocated or reserved would depend on
the data type of the variable being declared. For example, if a
variable is declared to be of integer type, then 32 bits of memory
storage will be reserved for that variable.
39.What is the advantage of the heap over a stack?
 The heap is more flexible than the stack. That’s because memory
space for the heap can be dynamically allocated and de-allocated as
needed. However, the memory of the heap can at times be slower
when compared to that stack.
40. What is a postfix expression?
 A postfix expression is an expression in which each operator follows
its operands. The advantage of this form is that there is no need to
group sub-expressions in parentheses or to consider operator
precedence.
41.What is Data abstraction?
 Data abstraction is a powerful tool for breaking down complex data
problems into manageable chunks. This is applied by initially
specifying the data objects involved and the operations to be
performed on these data objects without being overly concerned with
how the data objects will be represented and stored in memory.
42.How do you insert a new item in a binary search tree?
 Assuming that the data to be inserted is a unique value (that is, not an
existing entry in the tree), check first if the tree is empty. If it’s
empty, just insert the new item in the root node. If it’s not empty,
refer to the new item’s key. If it’s smaller than the root’s key, insert it

Dr.Maya Nayak
into the root’s left subtree, otherwise, insert it into the root’s right
subtree.
43.How does a selection sort work for an array?
 The selection sort is a fairly intuitive sorting algorithm, though not
necessarily efficient. In this process, the smallest element is first
located and switched with the element at subscript zero, thereby
placing the smallest element in the first position.
 The smallest element remaining in the subarray is then located next
to subscripts 1 through n-1 and switched with the element at
subscript 1, thereby placing the second smallest element in the
second position. The steps are repeated in the same manner till the
last element.
44.How do signed and unsigned numbers affect memory?
 In the case of signed numbers, the first bit is used to indicate whether
positive or negative, which leaves you with one bit short. With
unsigned numbers, you have all bits available for that number. The
effect is best seen in the number range (an unsigned 8-bit number has
a range 0-255, while the 8-bit signed number has a range -128 to
+127.
45.What is the minimum number of nodes that a binary tree can have?
 A binary tree can have a minimum of zero nodes, which occurs when
the nodes have NULL values. Furthermore, a binary tree can also
have 1 or 2 nodes.
46. What are dynamic data structures?
 Dynamic data structures are structures that expand and contract as a
program runs. It provides a flexible means of manipulating data
because it can adjust according to the size of the data.
47. In what data structures are pointers applied?
 Pointers that are used in linked list have various applications in the
data structure. Data structures that make use of this concept include
the Stack, Queue, Linked List and Binary Tree.
48.Do all declaration statements result in a fixed reservation in memory?
 Most declarations do, with the exemption of pointers. Pointer
declaration does not allocate memory for data, but for the address of

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the pointer variable. Actual memory allocation for the data comes
during run-time.
49.What are ARRAYs?
 When dealing with arrays, data is stored and retrieved using an index
that refers to the element number in the data sequence. This means
that data can be accessed in any order. In programming, an array is
declared as a variable having a number of indexed elements.
50.What is the minimum number of queues needed when implementing a priority
queue?
 The minimum number of queues needed in this case is two. One queue is
intended for sorting priorities while the other queue is used for actual storage
of data.
51.Which sorting algorithm is considered the fastest?
 There are many types of sorting algorithms: quick sort, bubble sort, balloon
sort, radix sort, merge sort, etc. Not one can be considered the fastest
because each algorithm is designed for a particular data structure and data
set. It would depend on the data set that you would want to sort.
52. Differentiate STACK from ARRAY?
 Stack follows a LIFO pattern. It means that data access follows a sequence
wherein the last data to be stored when the first one to be extracted. Arrays,
on the other hand, does not follow a particular order and instead can be
accessed by referring to the indexed element within the array.
53. Give a basic algorithm for searching a binary search tree?
 if the tree is empty, then the target is not in the tree, end search
 if the tree is not empty, the target is in the tree
 check if the target is in the root item
 if a target is not in the root item, check if a target is smaller than the
root’s value
 if a target is smaller than the root’s value, search the left subtree
 else, search the right subtree
54.What is a dequeue?

Dr.Maya Nayak
 A dequeue is a double-ended queue. This is a structure wherein
elements can be inserted or removed from either end.
55.What is a bubble sort and how do you perform it?
 A bubble sort is one sorting technique that can be applied to data
structures such as an array. It works by comparing adjacent elements
and exchanges their values if they are out of order. This method lets
the smaller values “bubble” to the top of the list, while the larger
value sinks to the bottom.
56.What are the parts of a linked list?
 A linked list typically has two parts: the head and the tail. Between the
head and tail lie the actual nodes. All these nodes are linked
sequentially.
57.How does selection sort work?
 Selection sort works by picking the smallest number from the list and
placing it at the front. This process is repeated for the second position
towards the end of the list. It is the simplest sort algorithm.
58.What is a graph?
 A graph is one type of data structure that contains a set of ordered
pairs. These ordered pairs are also referred to as edges or arcs and are
used to connect nodes where data can be stored and retrieved.
59.Differentiate linear from a nonlinear data structure.
 The linear data structure is a structure wherein data elements are
adjacent to each other. Examples of linear data structure include
arrays, linked lists, stacks, and queues. On the other hand, a non-linear
data structure is a structure wherein each data element can connect to
more than two adjacent data elements. Examples of nonlinear data
structure include trees and graphs.
60.What is an AVL tree?
 An AVL tree is a type of binary search tree that is always in a state of
partially balanced. The balance is measured as a difference between
the heights of the subtrees from the root. This self-balancing tree was
known to be the first data structure to be designed as such.
61.What are doubly linked lists?
 Doubly linked lists are a special type of linked list wherein traversal
across the data elements can be done in both directions. This is made

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possible by having two links in every node, one that links to the next
node and another one that connects to the previous node.
62.What is Huffman’s algorithm?
 Huffman’s algorithm is used for creating extended binary trees that
have minimum weighted path lengths from the given weights. It
makes use of a table that contains the frequency of occurrence for
each data element.
63.What is Fibonacci search?
 Fibonacci search is a search algorithm that applies to a sorted array. It
makes use of a divide-and-conquer approach that can significantly
reduce the time needed in order to reach the target element.
64.Briefly explain recursive algorithm?
 Recursive algorithm targets a problem by dividing it into smaller,
manageable sub-problems. The output of one recursion after
processing one sub-problem becomes the input to the next recursive
process.
65.How do you search for a target key in a linked list?
 To find the target key in a linked list, you have to apply sequential
search. Each node is traversed and compared with the target key, and
if it is different, then it follows the link to the next node. This traversal
continues until either the target key is found or if the last node is
reached.

Data structures

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