Data Structure Multiple Choice Questions and Answers
Array and Array Operations
This set of Data Structure Multiple Choice Questions & Answers (MCQs) focuses on “Array and Array Operations”.
1. Which of these best describes an array?
a) A data structure that shows a hierarchical behavior
b) Container of objects of similar types
c) Arrays are immutable once initialised
d) Array is not a data structure
View Answer
Explanation: Array contains elements only of the same type.
2. How do you initialize an array in C?
a) int arr[3] = (1,2,3);
b) int arr(3) = {1,2,3};
c) int arr[3] = {1,2,3};
d) int arr(3) = (1,2,3);
View Answer
Explanation: This is the syntax to initialize an array in C.
3. How do you instantiate an array in Java?
a) int arr[] = new int(3);
b) int arr[];
c) int arr[] = new int[3];
d) int arr() = new int(3);
View Answer
Explanation: Note that int arr[]; is declaration whereas int arr[] = new int[3]; is to instantiate an array.
4. Which of the following is the correct way to declare a multidimensional array in Java?
a) int[] arr;
b) int arr[[]];
c) int[][]arr;
d) int[[]] arr;
View Answer
Explanation: The syntax to declare multidimensional array in java is either int[][] arr; or int arr[][];
5. What is the output of the following Java code?
public class array
{
public static void main(String args[])
{
int []arr = {1,2,3,4,5};
System.out.println(arr[2]);
System.out.println(arr[4]);
}
}a) 3 and 5
b) 5 and 3
c) 2 and 4
d) 4 and 2
View Answer
Explanation: Array indexing starts from 0.
6. What is the output of the following Java code?
public class array
{
public static void main(String args[])
{
int []arr = {1,2,3,4,5};
System.out.println(arr[5]);
}
}a) 4
b) 5
c) ArrayIndexOutOfBoundsException
d) InavlidInputException
View Answer
Explanation: Trying to access an element beyond the limits of an array gives ArrayIndexOutOfBoundsException.
7. When does the ArrayIndexOutOfBoundsException occur?
a) Compile-time
b) Run-time
c) Not an error
d) Not an exception at all
View Answer
Explanation: ArrayIndexOutOfBoundsException is a run-time exception and the compilation is error-free.
8. Which of the following concepts make extensive use of arrays?
a) Binary trees
b) Scheduling of processes
c) Caching
d) Spatial locality
View Answer
Explanation: Whenever a particular memory location is referred to, it is likely that the locations nearby are also referred, arrays are stored as contiguous blocks in memory, so if you want to access array elements, spatial locality makes it to access quickly.
9. What are the advantages of arrays?
a) Objects of mixed data types can be stored
b) Elements in an array cannot be sorted
c) Index of first element of an array is 1
d) Easier to store elements of same data type
View Answer
Explanation: Arrays store elements of the same data type and present in continuous memory locations.
10. What are the disadvantages of arrays?
a) Data structure like queue or stack cannot be implemented
b) There are chances of wastage of memory space if elements inserted in an array are lesser than the allocated size
c) Index value of an array can be negative
d) Elements are sequentially accessed
View Answer
Explanation: Arrays are of fixed size. If we insert elements less than the allocated size, unoccupied positions can’t be used again. Wastage will occur in memory.
11. Assuming int is of 4bytes, what is the size of int arr[15];?
a) 15
b) 19
c) 11
d) 60
View Answer
Explanation: Since there are 15 int elements and each int is of 4bytes, we get 15*4 = 60bytes.
12. In general, the index of the first element in an array is __________
a) 0
b) -1
c) 2
d) 1
View Answer
Explanation: In general, Array Indexing starts from 0. Thus, the index of the first element in an array is 0.
13. Elements in an array are accessed _____________
a) randomly
b) sequentially
c) exponentially
d) logarithmically
View Answer
Explanation: Elements in an array are accessed randomly. In Linked lists, elements are accessed sequentially.
Stack Operations – 1
This set of Data Structure Multiple Choice Questions & Answers (MCQs) focuses on “Stack Operations – 1”.
1. Process of inserting an element in stack is called ____________
a) Create
b) Push
c) Evaluation
d) Pop
View Answer
Explanation: Push operation allows users to insert elements in the stack. If the stack is filled completely and trying to perform push operation stack – overflow can happen.
2. Process of removing an element from stack is called __________
a) Create
b) Push
c) Evaluation
d) Pop
View Answer
Explanation: Elements in the stack are removed using pop operation. Pop operation removes the top most element in the stack i.e. last entered element.
3. In a stack, if a user tries to remove an element from an empty stack it is called _________
a) Underflow
b) Empty collection
c) Overflow
d) Garbage Collection
View Answer
Explanation: Underflow occurs when the user performs a pop operation on an empty stack. Overflow occurs when the stack is full and the user performs a push operation. Garbage Collection is used to recover the memory occupied by objects that are no longer used.
a) Overflow
b) Crash
c) Underflow
d) User flow
View Answer
5. Entries in a stack are “ordered”. What is the meaning of this statement?
a) A collection of stacks is sortable
b) Stack entries may be compared with the ‘<‘ operation
c) The entries are stored in a linked list
d) There is a Sequential entry that is one by one
View Answer
Explanation: In stack data structure, elements are added one by one using push operation. Stack follows LIFO Principle i.e. Last In First Out(LIFO).
6. Which of the following is not the application of stack?
a) A parentheses balancing program
b) Tracking of local variables at run time
c) Compiler Syntax Analyzer
d) Data Transfer between two asynchronous process
View Answer
Explanation: Data transfer between the two asynchronous process uses the queue data structure for synchronisation. The rest are all stack applications.
7. Consider the usual algorithm for determining whether a sequence of parentheses is balanced. The maximum number of parentheses that appear on the stack AT ANY ONE TIME when the algorithm analyzes: (()(())(()))?
a) 1
b) 2
c) 3
d) 4 or more
View Answer
Explanation: In the entire parenthesis balancing method when the incoming token is a left parenthesis it is pushed into stack. A right parenthesis makes pop operation to delete the elements in stack till we get left parenthesis as top most element. 3 elements are there in stack before right parentheses comes. Therefore, maximum number of elements in stack at run time is 3.
8. Consider the usual algorithm for determining whether a sequence of parentheses is balanced. Suppose that you run the algorithm on a sequence that contains 2 left parentheses and 3 right parentheses (in some order). The maximum number of parentheses that appear on the stack AT ANY ONE TIME during the computation?
a) 1
b) 2
c) 3
d) 4 or more
View Answer
Explanation: In the entire parenthesis balancing method when the incoming token is a left parenthesis it is pushed into stack. A right parenthesis makes pop operation to delete the elements in stack till we get left parenthesis as top most element. 2 left parenthesis are pushed whereas one right parenthesis removes one of left parenthesis. 2 elements are there before right parenthesis which is the maximum number of elements in stack at run time.
9. What is the value of the postfix expression 6 3 2 4 + – *?
a) 1
b) 40
c) 74
d) -18
View Answer
Explanation: Postfix Expression is (6*(3-(2+4))) which results -18 as output.
10. Here is an infix expression: 4 + 3*(6*3-12). Suppose that we are using the usual stack algorithm to convert the expression from infix to postfix notation. The maximum number of symbols that will appear on the stack AT ONE TIME during the conversion of this expression?
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: When we perform the conversion from infix to postfix expression +, *, (, * symbols are placed inside the stack. A maximum of 4 symbols are identified during the entire conversion.
Stack Operations – 2
This set of Data Structure Interview Questions and Answers focuses on “Stack Operations – 2”.
1. The postfix form of the expression (A+ B)*(C*D- E)*F / G is?
a) AB+ CD*E – FG /**
b) AB + CD* E – F **G /
c) AB + CD* E – *F *G /
d) AB + CDE * – * F *G /
View Answer
Explanation: (((A+ B)*(C*D- E)*F) / G) is converted to postfix expression as
(AB+(*(C*D- E)*F )/ G)
(AB+CD*E-*F) / G
(AB+CD*E-*F * G/). Thus Postfix expression is AB+CD*E-*F*G/
2. The data structure required to check whether an expression contains a balanced parenthesis is?
a) Stack
b) Queue
c) Array
d) Tree
View Answer
Explanation: The stack is a simple data structure in which elements are added and removed based on the LIFO principle. Open parenthesis is pushed into the stack and a closed parenthesis pops out elements till the top element of the stack is its corresponding open parenthesis. If the stack is empty, parenthesis is balanced otherwise it is unbalanced.
3. What data structure would you mostly likely see in non recursive implementation of a recursive algorithm?
a) Linked List
b) Stack
c) Queue
d) Tree
View Answer
Explanation: In recursive algorithms, the order in which the recursive process comes back is the reverse of the order in which it goes forward during execution. The compiler uses the stack data structure to implement recursion. In the forwarding phase, the values of local variables, parameters and the return address are pushed into the stack at each recursion level. In the backing-out phase, the stacked address is popped and used to execute the rest of the code.
4. The process of accessing data stored in a serial access memory is similar to manipulating data on a ________
a) Heap
b) Binary Tree
c) Array
d) Stack
View Answer
Explanation: In serial access memory data records are stored one after the other in which they are created and are accessed sequentially. In stack data structure, elements are accessed sequentially. Stack data structure resembles the serial access memory.
5. The postfix form of A*B+C/D is?
a) *AB/CD+
b) AB*CD/+
c) A*BC+/D
d) ABCD+/*
View Answer
Explanation: Infix expression is (A*B)+(C/D)
AB*+(C/D)
AB*CD/+. Thus postfix expression is AB*CD/+.
6. Which data structure is needed to convert infix notation to postfix notation?
a) Branch
b) Tree
c) Queue
d) Stack
View Answer
Explanation: The Stack data structure is used to convert infix expression to postfix expression. The purpose of stack is to reverse the order of the operators in the expression. It also serves as a storage structure, as no operator can be printed until both of its operands have appeared.
7. The prefix form of A-B/ (C * D ^ E) is?
a) -/*^ACBDE
b) -ABCD*^DE
c) -A/B*C^DE
d) -A/BC*^DE
View Answer
Explanation: Infix Expression is (A-B)/(C*D^E)
(-A/B)(C*D^E)
-A/B*C^DE. Thus prefix expression is -A/B*C^DE.
8. What is the result of the following operation?
Top (Push (S, X))
a) X
b) X+S
c) S
d) XS
View Answer
Explanation: The function Push(S,X) pushes the value X in the stack S. Top() function gives the value which entered last. X entered into stack S at last.
9. The prefix form of an infix expression (p + q) – (r * t) is?
a) + pq – *rt
b) – +pqr * t
c) – +pq * rt
d) – + * pqrt
View Answer
Explanation: Given Infix Expression is ((p+q)-(r*t))
(+pq)-(r*t)
(-+pq)(r*t)
-+pq*rt. Thus prefix expression is -+pq*rt.
10. Which data structure is used for implementing recursion?
a) Queue
b) Stack
c) Array
d) List
View Answer
Explanation: Stacks are used for the implementation of Recursion.
Stack Operations – 3
This set of Data Structure Questions and Answers for Freshers focuses on “Stack Operations – 3”.
5. Consider the following operation performed on a stack of size 5.
Push(1);Pop();Push(2);Push(3);Pop();Push(4);Pop();Pop();Push(5);
Queue Operation
This set of Data Structure Multiple Choice Questions & Answers (MCQs) focuses on “Queue Operations”.
Singly Linked List Operations – 1
2. Consider an implementation of unsorted singly linked list. Suppose it has its representation with a head pointer only. Given the representation, which of the following operation can be implemented in O(1) time?
i) Insertion at the front of the linked listii) Insertion at the end of the linked listiii) Deletion of the front node of the linked listiv) Deletion of the last node of the linked list
9. Consider the following definition in c programming language.
struct node{int data;struct node * next;}typedef struct node NODE;NODE *ptr;
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