Answer Posted / janani

Data Structures Interview Questions Set -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.
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
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.
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.
What are the methods available in storing sequential files ?
Straight merging, Natural merging, Polyphase sort,
Distribution of Initial runs.
List out few of the Application of tree data-structure?
The manipulation of Arithmetic expression, Symbol Table
construction, Syntax analysis.
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.
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.
Does the minimum spanning tree of a graph give the shortest
distance between any 2 specified nodes?
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.
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.
What is the quickest sorting method to use?
The answer depends on what you mean by quickest. For most
sorting problems, it just doesn't matter how quick the sort
is because it is done infrequently or other operations take
significantly more time anyway. Even in cases in which
sorting speed is of the essence, there is no one answer. It
depends on not only the size and nature of the data, but
also the likely order. No algorithm is best in all cases.
There are three sorting methods in this author's toolbox
that are all very fast and that are useful in different
situations. Those methods are quick sort, merge sort, and
radix sort.

The Quick Sort
The quick sort algorithm is of the divide and conquer type.
That means it works by reducing a sorting problem into
several easier sorting problems and solving each of them. A
dividing value is chosen from the input data, and the data
is partitioned into three sets: elements that belong before
the dividing value, the value itself, and elements that
come after the dividing value. The partitioning is
performed by exchanging elements that are in the first set
but belong in the third with elements that are in the third
set but belong in the first Elements that are equal to the
dividing element can be put in any of the three sets the
algorithm will still work properly.

The Merge Sort
The merge sort is a divide and conquer sort as well. It
works by considering the data to be sorted as a sequence of
already-sorted lists (in the worst case, each list is one
element long). Adjacent sorted lists are merged into larger
sorted lists until there is a single sorted list containing
all the elements. The merge sort is good at sorting lists
and other data structures that are not in arrays, and it
can be used to sort things that don't fit into memory. It
also can be implemented as a stable sort.

The Radix Sort
The radix sort takes a list of integers and puts each
element on a smaller list, depending on the value of its
least significant byte. Then the small lists are
concatenated, and the process is repeated for each more
significant byte until the list is sorted. The radix sort
is simpler to implement on fixed-length data such as ints.
How can I search for data in a linked list?
Unfortunately, the only way to search a linked list is with
a linear search, because the only way a linked list's
members can be accessed is sequentially. Sometimes it is
quicker to take the data from a linked list and store it in
a different data structure so that searches can be more
efficient.
What is the heap?
The heap is where malloc(), calloc(), and realloc() get
memory.

Getting memory from the heap is much slower than getting it
from the stack. On the other hand, the heap is much more
flexible than the stack. Memory can be allocated at any
time and deallocated in any order. Such memory isn't
deallocated automatically; you have to call free().
Recursive data structures are almost always implemented
with memory from the heap. Strings often come from there
too, especially strings that could be very long at runtime.
If you can keep data in a local variable (and allocate it
from the stack), your code will run faster than if you put
the data on the heap. Sometimes you can use a better
algorithm if you use the heap faster, or more robust, or
more flexible. Its a tradeoff.
If memory is allocated from the heap, its available until
the program ends. That's great if you remember to
deallocate it when you're done. If you forget, it's a
problem. A �memory leak is some allocated memory that's no
longer needed but isn't deallocated. If you have a memory
leak inside a loop, you can use up all the memory on the
heap and not be able to get any more. (When that happens,
the allocation functions return a null pointer.) In some
environments, if a program doesn't deallocate everything it
allocated, memory stays unavailable even after the program
ends.
What is the easiest sorting method to use?
The answer is the standard library function qsort(). It's
the easiest sort by far for several reasons:
It is already written.
It is already debugged.
It has been optimized as much as possible (usually).
Void qsort(void *buf, size_t num, size_t size, int (*comp)
(const void *ele1, const void *ele2));




Data Structures Interview Questions Set -2

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.
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.
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.
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.
What is a node class?
A node class is a class that, relies on the base class for
services and implementation, provides a wider interface to
users than its base class, relies primarily on virtual
functions in its public interface depends on all its direct
and indirect base class can be understood only in the
context of the base class can be used as base for further
derivation
can be used to create objects. A node class is a class that
has added new services or functionality beyond the services
inherited from its base class.
When can you tell that a memory leak will occur?
A memory leak occurs when a program loses the ability to
free a block of dynamically allocated memory.
What is placement new?
When you want to call a constructor directly, you use the
placement new. Sometimes you have some raw memory that’s
already been allocated, and you need to construct an object
in the memory you have. Operator new’s special version
placement new allows you to do it.
class Widget
{
public :
Widget(int widgetsize);
…
Widget* Construct_widget_int_buffer(void *buffer,int
widgetsize)
{
return new(buffer) Widget(widgetsize);
}
};
This function returns a pointer to a Widget object that’s
constructed within the buffer passed to the function. Such
a function might be useful for applications using shared
memory or memory-mapped I/O, because objects in such
applications must be placed at specific addresses or in
memory allocated by special routines.
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
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.
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.
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
Tell how to check whether a linked list is circular ?
Create two pointers, each set to the start of the list.
Update each as follows:

while (pointer1)

{
pointer1 = pointer1->next;
pointer2 = pointer2->next; if (pointer2) pointer2=pointer2-
>next;
if (pointer1 == pointer2)

? ? ? ? ? ? {
print (\”circular\n\”);
}
}
What is the difference between ARRAY and STACK?
STACK follows LIFO. Thus the item that is first entered
would be the last removed.

In array the items can be entered or removed in any order.
Basically each member access is done using index. No strict
order is to be followed here to remove a particular element.
What is the difference between NULL AND VOID pointer?
NULL can be value for pointer type variables.
VOID is a type identifier which has not size.
NULL and void are not same. Example: void* ptr = NULL;
What is precision?
Precision refers the accuracy of the decimal portion of a
value. Precision is the number of digits allowed after the
decimal point.
What is impact of signed numbers on the memory?
Sign of the number is the first bit of the storage
allocated for that number. So you get one bit less for
storing the number. For example if you are storing an 8-bit
number, without sign, the range is 0-255. If you decide to
store sign you get 7 bits for the number plus one bit for
the sign. So the range is -128 to +127.
How memory is reserved using a declaration statement ?
Memory is reserved using data type in the variable
declaration. A programming language implementation has
predefined sizes for its data types.

For example, in C# the declaration int i; will reserve 32
bits for variable i.

A pointer declaration reserves memory for the address or
the pointer variable, but not for the data that it will
point to. The memory for the data pointed by a pointer has
to be allocated at runtime.

The memory reserved by the compiler for simple variables
and for storing pointer address is allocated on the stack,
while the memory allocated for pointer referenced data at
runtime is allocated on the heap.
How many parts are there in a declaration statement?








Data Structures Interview Questions Set -3

There are two main parts, variable identifier and data type
and the third type is optional which is type qualifier like
signed/unsigned.
Is Pointer a variable?
Yes, a pointer is a variable and can be used as an element
of a structure and as an attribute of a class in some
programming languages such as C++, but not Java. However,
the contents of a pointer is a memory address of another
location of memory, which is usually the memory address of
another variable, element of a structure, or attribute of a
class.
What is Data Structure?
A data structure is a group of data elements grouped
together under one name. These data elements, known as
members, can have different types and different lengths.
Some are used to store the data of same type and some are
used to store different types of data.
What is significance of ” * ” ?
The symbol “*” tells the computer that you are declaring a
pointer.
Actually it depends on context.
In a statement like int *ptr; the ‘*’ tells that you are
declaring a pointer.
In a statement like int i = *ptr; it tells that you want to
assign value pointed to by ptr to variable i.

The symbol “*” is also called as Indirection Operator/
Dereferencing Operator.
Why do we Use a Multidimensional Array?
A multidimensional array can be useful to organize
subgroups of data within an array. In addition to
organizing data stored in elements of an array, a
multidimensional array can store memory addresses of data
in a pointer array and an array of pointers.

Multidimensional arrays are used to store information in a
matrix form.
e.g. a railway timetable, schedule cannot be stored as a
single dimensional array.
One can use a 3-D array for storing height, width and
length of each room on each floor of a building.
How do you assign an address to an element of a pointer
array ?
We can assign a memory address to an element of a pointer
array by using the address operator, which is the ampersand
(&), in an assignment statement such as ptemployee[0] =
&projects[2];
Run Time Memory Allocation is known as ?
Allocating memory at runtime is called a dynamically
allocating memory. In this, you dynamically allocate memory
by using the new operator when declaring the array, for
example : int grades[] = new int[10];
What method is used to place a value onto the top of a
stack?
push() method, Push is the direction that data is being
added to the stack. push() member method places a value
onto the top of a stack.
What method removes the value from the top of a stack?
The pop() member method removes the value from the top of a
stack, which is then returned by the pop() member method to
the statement that calls the pop() member method.
What does isEmpty() member method determines?
isEmpty() checks if the stack has at least one element.
This method is called by Pop() before retrieving and
returning the top element.
What is a queue ?
A Queue is a sequential organization of data. A queue is a
first in first out type of data structure. An element is
inserted at the last position and an element is always
taken out from the first position.
What is the relationship between a queue and its underlying
array?
Data stored in a queue is actually stored in an array. Two
indexes, front and end will be used to identify the start
and end of the queue.

When an element is removed front will be incremented by 1.
In case it reaches past the last index available it will be
reset to 0. Then it will be checked with end. If it is
greater than end queue is empty.

When an element is added end will be incremented by 1. In
case it reaches past the last index available it will be
reset to 0. After incrementing it will be checked with
front. If they are equal queue is full.
Which process places data at the back of the queue?
Enqueue is the process that places data at the back of the
queue.
Why is the isEmpty() member method called?
The isEmpty() member method is called within the dequeue
process to determine if there is an item in the queue to be
removed i.e. isEmpty() is called to decide whether the
queue has at least one element. This method is called by
the dequeue() method before returning the front element.
How is the front of the queue calculated ?
The front of the queue is calculated by front = (front+1) %
size.
What does each entry in the Link List called?
Each entry in a linked list is called a node. Think of a
node as an entry that has three sub entries. One sub entry
contains the data, which may be one attribute or many
attributes. Another points to the previous node, and the
last points to the next node. When you enter a new item on
a linked list, you allocate the new node and then set the
pointers to previous and next nodes.
What is Linked List ?
Linked List is one of the fundamental data structures. It
consists of a sequence of? nodes, each containing arbitrary
data fields and one or two (”links”) pointing to the next
and/or previous nodes. A linked list is a self-referential
datatype because it contains a pointer or link to another
data of the same type. Linked lists permit insertion and
removal of nodes at any point in the list in constant time,
but do not allow random access.
What member function places a new node at the end of the
linked list?
The appendNode() member function places a new node at the
end of the linked list. The appendNode() requires an
integer representing the current data of the node.
How is any Data Structure application is classified among
files?
A linked list application can be organized into a header
file, source file and main application file. The first file
is the header file that contains the definition of the NODE
structure and the LinkedList class definition. The second
file is a source code file containing the implementation of
member functions of the LinkedList class. The last file is
the application file that contains code that creates and
uses the LinkedList class.
Which file contains the definition of member functions?
Definitions of member functions for the Linked List class
are contained in the LinkedList.cpp file.
What are the major data structures used in the following
areas : RDBMS, Network data model & Hierarchical data model.
1. RDBMS Array (i.e. Array of structures)
2. Network data model Graph
3. Hierarchical data model Trees.
Difference between calloc and malloc ?
malloc: allocate n bytes
calloc: allocate m times n bytes initialized to 0

List some applications of multilinked structures?

613

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Why is arraylist not thread safe?

596

---

What is the best time complexity of bubble sort?

602

---

How many times is merge sort called?

601

---

Which sorting is best and why?

573

---

---

What is the logic to reverse the array?

550

---

In what areas do data structures applied?

579

---

What does args stand for?

554

---

Can arraylist contain duplicates?

565

---

write an algorithm to show the procedure of insertion into a b-tree?

597

---

What is a hashmap in c?

568

---

How would you dynamically allocate a one-dimensional and two-dimensional array of integers?

661

---

What is the minimum number of queues needed when implementing a priority queue?

630

---

How do you sort a collection in descending order?

621

---

Now you are given an array of a characters (both ASCII and Kanji) and, an index into the array. The index points to the start of some character. Now you need to write a function to do a backspace (i.e. delete the character before the given index).

615

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