# Data Structure Interview Questions & Answers

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

2. Whether Linked List is linear or Non-linear data structure?

3. Define Simulation?

Simulation is the process of forming an abstract model from a real situation in order to understand the impact of modifications and the effect of introducing various strategies on the situation.

4. What is the difference between Storage structure and file structure?

The representation of a particular data structure in the memory of a computer is called a storage structure whereas a storage structure representation in auxiliary memory is often called a file structure.

5. 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.

6. What is binary tree?

A binary tree is a tree in which every node has exactly two links i.e left and right link

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

if the balance factor of any node is other than 0 or 1 or -1 then balancing is done.

8. Which process places data at the back of the queue?

Enqueue is the process that places data at the back of the queue.

9. 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.

array may be multidiamensional or onediamensional

but stack should be onediamensional.

but both are linear data structure.

10. Define and explain ?push? and ?pop??

The insertion operation is referred to as ?push? and the deletion operation is referred to as ?pop?. Since, insertion and deletion operations are performed at one end of the stack; the elements can only be removed in the opposite order from that in which they were added to the stack. This phenomenon is observed in conjunction with recursive functions.

11. 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.

12. What are the various kinds of sorting techniques? Which is has best case?

Bubble sort,Quick sort,Insertion sort,Selection sort Merge sort,Heap sort Among the sorting algorithms quick sort is the best one

heap sort is the best sorting technique bccoz its complexity in best case ,worst and avg case is of O(nlogn)

in worst case quick sort the complexity in best case and avg case is of O(nlogn) and worst case O(n^2)

13. 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.

14. 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 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));

Quick sort is faster and easy sorting technique compare than other sorting technique.

worst time Olog(n2)

Avg time Olog(n log n)

15. Why is the isEmpty() member method called?

pop() is one of the most important operation performed onto the stack. This operation remove the topmost element from the stack. But for that we must have to check stack is empty or not. If stack is empty & we are going to perform pop() operation at that time it underflows therefore while doing pop() operation we have to check stack is empty or not this work is done by calling isEmpty() method

16. 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.

17. 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.

18. 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.

19. What is the bubble short?

Bubble sort is a sorting algorithm, where every element in the unsorted list, is compared with every other element to make a sorted list. All these comparisons add up to the overall time complexity of the algorithm to be O(n) if n is the input size, which is really high compared to other popular algorithms.

20. What is the stack?

Stack is a linear data-structure which operates as LIFO(last-in-first-out)manner.which contains PUSH(),POP() as standard subroutines and SEEK() as non-standard subroutine.And also it contain all the recursive calls information in the LIFO order.

stack is ordered data structure.

Stack operations are based on LIFO(LAST IN FIRST OUT)concepts.

There are mainly two operations. they are,

1.PUSH-insert element into stack

2.POP0- remove elements form stack

insertion and deletion take at one end is known as TOP.

21. 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.

22. How many parts are there in a declaration statement?

There are two main parts, variable identifier and data type and the third type is optional which is type qualifier like signed/unsigned.

23. What is the difference between NULL and VOID pointer?

NULL pointer refer to give the value for pointer type variable

but VOID refer that it return the null value

24. 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.

25. 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.

26. 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.

27. 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.

28. 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.

29. 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.

30. 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.

31. What is Heap data structure?

The binary heap data structure is an array that can be viewed as a complete binary tree.

Each node of the binary tree corresponds to an element of the array.

The array is completely filled on all levels except possibly lowest.

32. 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

33. 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.

34. What is a priority queue?

Waiting queue may not operate on a strictly first in first out basis, but on some complex priority scheme based on such factors as what compiler is being used, the execution time required, number of print lines, etc. The resulting queue is called a priority queue.

35. What are the methods available in storing sequential files?

Straight merging, Natural merging, Polyphase sort, Distribution of Initial runs.

36. Which file contains the definition of member functions?

Definitions of member functions for the Linked List class are contained in the LinkedList.cpp file.

37. 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.

38. Which one is faster? A binary search of an ordered set of elements in an array or a sequential search of the elements.

Binary search is faster because we traverse the elements by using the policy of Divide and Conquer. we compare the key element with the approximately center element, if it is smaller than it search is applied in the smaller elements only otherwise the search is applied in the larger set of elements. its complexity is as we all know is log n as compared to the sequential one whose complexity is n.

39. Whether Linked List is linear or Non-linear data structure?

According to Access strategies Linked list is a linear one.

40. How to concatenate two linked lists?

By changing the null pointer of the first linked list to point the header of the second linked list.

41. 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.

42. How many parts are there in a declaration statement?

There are two main parts, variable identifier and data type and the third type is optional

which is type qualifier like signed/unsigned.

43. What happens if i call free() twice?

nothing will happend. when you call for first time it will free’s the memory which is in hold,but in second time it wont do anything because the memory is already released

44. What is the quickest sorting method to use?

he 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 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.

45. How is the front of the queue calculated ?

The front of the queue is calculated by front = (front+1) % size.

46. 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.

47. How can a node be inserted in the middle of a linked list?

By repointing the previous and the next elements of existing nodes to the new node. You can insert a

node in the middle of a linked list by repointing the previous and the next elements of existing nodes to the new node.

48. explain behaviour of code void *ptr ; ptr = malloc(0); if(ptr)pf(“Valid”); else pf(“Invalid”);

op: Invalid

because malloc function returns null when size is 0, hence ptr=null value.. so else part gets executed

49. What is a one way chain or singly linked linear list?

Singly linked list is a collection of nodes. Each node has element and address of the next element. With that address only forward traversal is possible i.e. single link

50. What exactly does this procedure BUBBLE_SORT (K, N) does?

This procedure takes input as the array K and number of elements in the array N. And sorts the N elements in either ascending or descending order.

51. How to concatenate the two linked lists?

perform given operation,

Last node of first link list–> next = First node of second link list

52. 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.

53. Name two desirable properties of hashing functions.

Some of the desirable properties of a hashing function are speed and the generation of addresses uniformly.

54. 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.

55. Suppose you have a sorted array of 250 elements. What is the maximum number of elements you have to examine to determine if some value v is in your array if you use an efficient search? a) 7 b) 8 c) 125 d) 250

Use binary search then number of examine will be lg(250)~8

56. What is linear hashing?

In linear hashing, the table is gradually expanded by splitting the buckets in order until the table has doubled its size.

57. 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.

58. Explain the three applications in which stacks are used?

The first application majorly deals with the recursion, the second application is a classical and the last one is known as stack machines which chiefly deals with insertion and deletion from the stack.

1) recursion

2) Expression evaluation and syntax parsing

3) runtime memory management

59. Given N discs of decreasing size stacked on one needle and two empty needles, it is required to stack all the discs onto a second needle in decreasing order of size. The third needle may be used as temporary storage. The movement of the discs is restricted by the following rules (1) A disc may be moved from any needle to any other (2) Only one disc may be moved at a time (3) At no time may a larger disc rest upon smaller disc explain the solution?

The solution to this problem is most clearly seen with the aid of induction, to move one disc, merely move it from needle A to needle C. To move two discs, move the first disc to needle B, move the second from needle A to needle C, then move the disc from needle B to needle C.

60. Why is the isEmpty() member method called? What is the heap?

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.

61. 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.

62. 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

63. 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.

We have to pop the stack to get the values inside the stack and to get a value in the top of an empty stack we have to peep out.

64. What is the distant relationship between a list structure and a digraph?

In particular, a list is a directed graph with one source node corresponding to the entire list and with every node immediately connected to the source code.

65. What is Data Structure?

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.

66. Define Index area and its subdivisions?

Index area is created automatically by the data-management routines in the operating systems. A number of index levels may be involved in an indexed sequential file. The lowest of index is the track index, which is always written on the first track of the cylinders for the indexed sequential file. The track index contains two entries for each prime track of the cylinder a normal entry and an overflow entry.

67. What do you mean by asymptotic notation?

68. 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.

69. Name the data structure used to maintain file identification?

70. 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.

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.

72. How do you assign an address to an element of a pointer array ?

address operator, which is the ampersand (&), in an assignment statement such as ptemployee[0] = &projects[2];

73. Define data structure in terms of relation?

The possible ways in which the data items or atoms are logically related define different data structures.

74. 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.

There are many data structures which can be represented so as to permit the referencing of any element by knowing its position in the structure. The selection operation associated with such a structure is said to possess an addressing function. An addressing function for a data structure consisting of n elements is a function which maps the ith element of the data structure onto an integer between one and n. In the case of a vector, the addressing function f maps the ith element onto the integer I, which is a linear addressing function.

76. 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.

77. Define an addressing function for a data structure?

An addressing function for a data structure consisting of n elements is a function which maps the ith element of the data structure onto an integer between one and n. In the case of a vector, the addressing function f maps the ith element onto the integer (i).

78. What is splitting?

Splitting refers to the rehashing of a bucket b and its overflow in order to distribute the keys in them among b and one other primary location.

79. 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];

80. How do you define a vector for a data structure?

The simplest data structure that makes use of computed address to locate its elements is the one ? dimensional array and is called as a vector.

81. 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.

82. 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.

A linked list is a data structure which contains two nodes

1.INFO

INFO contains address of starting element.

84. 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.

85. What is event, delegate & data structure?

Event:Event is the state change of a component.Events provides users to communicate with the computer applications such as mouse events,keyboadr events etc.

Delegate:Delegate is a new model to provide events with the help of event source and event listener,in the event source generates an event then the rigistered listener receives those event and implement that event

Data structure:Data structure is a logical unit which provides the way to storage and organization of data on the memory of a computer

86. What is data structure?

A data structure is a particular way of storing and organizing data in a computer so that it can be used efficiently

87. 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.

88. State the theorem which is used to determine whether a given expression is valid or not.

A polish suffix formula is well formed if and only if the rank of the formula is ?one? and the rank of any proper head of a polish formula is greater than or equal to ?one?.

89. Define stack?

An important sub class of lists permits the insertion or deletion of an element to occur only at one end. A linear list belonging to this sub class is called a stack.

90. State procedure in accordance with function?

A procedure is similar to a function but there is no value returned explicitly. A procedure is also invoked differently. Where there are parameters, a procedure returns its results through the parameters

91. Tell how to check whether a linked list is circular?

void iscircular()

{

node *p,*comp;

p=comp=start;

while(p)

{

if(comp==p)

cout<<“circular”;

}

}

92. What is abstract data type?

The Abstract data type is a specification of data types which are having some defined set of operations and which are independent of their implementation.

example :stack is an Abstract data type. But stack implemented with an array and with linked list are both different data structures.

93. What is tree? Define with example

A tree is a nonlinear data structure which follows a parent child(hierarchal) relationship. It has a root node from which tree is spawn. rest all other nodes are either parent nodes or child nodes.

94. How many types of data structures are there?

95. What is data struct?

struct is a keyword used for designing structure data type. Structure is the collection of multiple datatypes in one datatype to make your access easy.

96.