1Which data structure follows the LIFO (Last In First Out) principle?
A.Stack
B.Queue
C.Linked List
D.Tree
Correct Answer: Stack
Explanation:
A stack follows the LIFO principle, meaning the last element added is the first one to be removed.
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2In a stack implemented using an array of size N, what is the condition for stack overflow?
A.top == N
B.top == 0
C.top == N - 1
D.top == -1
Correct Answer: top == N - 1
Explanation:
In a 0-indexed array, the last index is N-1. If the top pointer reaches N-1, no more elements can be pushed, indicating an overflow.
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3What is the time complexity of the push operation in a stack implemented using an array?
A.O(1)
B.O(log n)
C.O(n)
D.O(n^2)
Correct Answer: O(1)
Explanation:
Pushing onto a stack involves incrementing the top pointer and assigning a value, which takes constant time O(1).
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4Which operation removes the top element from the stack?
A.Push
B.Traverse
C.Peek
D.Pop
Correct Answer: Pop
Explanation:
The Pop operation removes the element currently at the top of the stack and decrements the top pointer.
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5In a linked list representation of a stack, where are elements pushed and popped from?
A.The middle of the list
B.The head of the list
C.Random positions
D.The tail of the list
Correct Answer: The head of the list
Explanation:
Inserting and deleting from the head of a linked list is O(1), making it the most efficient end to represent the top of the stack.
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6What happens if you try to pop an element from an empty stack?
A.Garbage Value
B.System Crash
C.Stack Underflow
D.Stack Overflow
Correct Answer: Stack Underflow
Explanation:
Stack Underflow occurs when an attempt is made to remove an item from a stack that contains no elements.
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7Which pointer is used to track the last element added to a stack?
A.Front
B.Head
C.Rear
D.Top
Correct Answer: Top
Explanation:
The 'Top' pointer always points to the most recently added element in the stack.
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8What is the result of evaluating the postfix expression: 5 3 + 2 * ?
A.10
B.13
C.16
D.25
Correct Answer: 16
Explanation:
5 + 3 = 8. Then 8 * 2 = 16.
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9Another name for Reverse Polish Notation (RPN) is:
A.Affine Notation
B.Prefix Notation
C.Postfix Notation
D.Infix Notation
Correct Answer: Postfix Notation
Explanation:
Reverse Polish Notation places operators after their operands, which is the definition of Postfix Notation.
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10Convert the infix expression (A + B) * C into postfix.
A.A B C + *
B.A + B C *
C.+ A B * C
D.A B + C *
Correct Answer: A B + C *
Explanation:
The parentheses force A+B to be evaluated first (AB+), followed by multiplication with C (AB+C*).
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11Which data structure is primarily used to convert infix expressions to postfix expressions?
A.Graph
B.Stack
C.Heap
D.Queue
Correct Answer: Stack
Explanation:
A stack is used to hold operators and manage their precedence during the conversion from infix to postfix.
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12In Polish notation (Prefix), where is the operator placed?
A.Between the operands
B.At the end of the expression
C.After the operands
D.Before the operands
Correct Answer: Before the operands
Explanation:
In Prefix (Polish) notation, the operator precedes the operands (e.g., +AB).
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13What is the prefix form of the expression: A + B * C ?
A.* + A B C
B.A B C * +
C.+ * A B C
D.+ A * B C
Correct Answer: + A * B C
Explanation:
Multiplication has higher precedence: BC becomes BC. Then addition: + A (*BC).
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14When evaluating a postfix expression, what do you do when you encounter an operand?
A.Ignore it
B.Push onto stack
C.Pop from stack
D.Evaluate immediately
Correct Answer: Push onto stack
Explanation:
Operands are pushed onto the stack. When an operator is encountered, operands are popped to perform the calculation.
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15Which operator has the highest precedence among the following?
A.+
B.-
C.*
D.^ (Exponentiation)
Correct Answer: ^ (Exponentiation)
Explanation:
Exponentiation typically has higher precedence than multiplication, division, addition, and subtraction.
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16The associativity of the exponentiation operator (^) is usually:
A.Right to Left
B.Non-associative
C.Random
D.Left to Right
Correct Answer: Right to Left
Explanation:
In most contexts, 2^3^2 is evaluated as 2^(3^2), which is Right to Left.
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17Which data structure follows the FIFO (First In First Out) principle?
A.Stack
B.Queue
C.Graph
D.Tree
Correct Answer: Queue
Explanation:
A Queue adds elements to the rear and removes them from the front, following FIFO.
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18The operation of adding an element to a queue is called:
A.Push
B.Pop
C.Dequeue
D.Enqueue
Correct Answer: Enqueue
Explanation:
Enqueue is the standard term for inserting an element into a queue.
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19In an array implementation of a simple queue, which pointers are maintained?
A.Start and End
B.Front and Rear
C.Top only
D.Head and Tail
Correct Answer: Front and Rear
Explanation:
Front tracks the first element (for deletion), and Rear tracks the last element (for insertion).
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20What is the initial value of Front and Rear in an empty queue (array implementation)?
A.-1
B.Null
C.1
D.0
Correct Answer: -1
Explanation:
Traditionally, -1 indicates that the pointers refer to no valid index in the array.
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21In a linear queue array implementation, a queue is empty when:
A.Front == -1
B.Rear == Max - 1
C.Front == 0
D.Front == Rear
Correct Answer: Front == -1
Explanation:
If Front is -1 (and usually Rear is also -1), the queue contains no elements.
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22What is the major drawback of a simple linear queue implemented with an array?
A.It cannot handle integers
B.Empty spaces created by dequeue cannot be reused
C.It is slow
D.It uses too much memory
Correct Answer: Empty spaces created by dequeue cannot be reused
Explanation:
Once Rear reaches the end of the array, no more elements can be added even if space exists at the beginning due to previous dequeues.
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23Which data structure resolves the memory wastage issue of a linear queue?
A.Tree
B.Priority Queue
C.Stack
D.Circular Queue
Correct Answer: Circular Queue
Explanation:
A Circular Queue connects the end of the array back to the beginning, allowing reuse of empty spaces.
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24In a Circular Queue of size N, the condition for the queue being full is:
A.Rear == N - 1
B.Front == 0
C.(Rear + 1) % N == Front
D.Front == Rear + 1
Correct Answer: (Rear + 1) % N == Front
Explanation:
This formula checks if the next position after Rear wraps around to the current Front, indicating the buffer is full.
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25In a linked list implementation of a queue, where is the Enqueue operation performed?
A.At the Tail (Rear)
B.At the Head
C.At the Middle
D.Randomly
Correct Answer: At the Tail (Rear)
Explanation:
To maintain FIFO, new elements enter at the end (Rear) of the list.
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26What is the time complexity for Dequeue operation in a linked list implementation (assuming a head pointer)?
A.O(1)
B.O(n)
C.O(log n)
D.O(n^2)
Correct Answer: O(1)
Explanation:
Removing from the head of a linked list requires just pointer adjustment, which is constant time.
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27A queue where elements are removed based on a specific value rather than arrival time is called:
A.Priority Queue
B.Linear Queue
C.Circular Queue
D.Deque
Correct Answer: Priority Queue
Explanation:
In a Priority Queue, elements are served based on priority (highest or lowest value), not just FIFO.
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28Which data structure is most efficient for implementing a Priority Queue?
A.Binary Heap
B.Array
C.Stack
D.Linked List
Correct Answer: Binary Heap
Explanation:
A Binary Heap allows insertion and deletion of the highest priority element in O(log n) time, which is generally more efficient than sorted arrays or lists.
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29In an Ascending Priority Queue, which element is removed first?
A.The smallest number
B.The last number inserted
C.The largest number
D.The first number inserted
Correct Answer: The smallest number
Explanation:
In an ascending priority queue, the smallest item has the highest priority and is removed first.
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30What does 'Deque' stand for?
A.Dynamic Queue
B.Dedicated Queue
C.Double Ended Queue
D.Data Queue
Correct Answer: Double Ended Queue
Explanation:
Deque is an abbreviation for Double Ended Queue.
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31What is a characteristic feature of a Deque?
A.Elements are always sorted
B.Insertion and deletion allowed at both ends
C.Insertion and deletion at one end only
D.Insertion at one end, deletion at the other
Correct Answer: Insertion and deletion allowed at both ends
Explanation:
A Deque allows operations (insert/delete) at both the Front and the Rear.
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32An Input-Restricted Deque allows:
A.Insertion at one end, deletion at both ends
B.Insertion and deletion at one end
C.Insertion at both ends, deletion at one end
D.Insertion and deletion at both ends
Correct Answer: Insertion at one end, deletion at both ends
Explanation:
Input-Restricted means input (insertion) is restricted to one end, but deletion is allowed at both.
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33An Output-Restricted Deque allows:
A.Insertion and deletion at both ends
B.Insertion and deletion at one end
C.Insertion at both ends, deletion at one end
D.Insertion at one end, deletion at both ends
Correct Answer: Insertion at both ends, deletion at one end
Explanation:
Output-Restricted means output (deletion) is restricted to one end, but insertion is allowed at both.
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34If you implement a Stack using two Queues, what is the cost of the Push operation usually made to be?
A.O(log n)
B.O(n^2)
C.O(n)
D.O(1)
Correct Answer: O(n)
Explanation:
To maintain LIFO behavior using FIFO queues, one operation (usually push) becomes expensive O(n) to rearrange elements.
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35Which of the following is an application of a Stack?
A.CPU process scheduling
B.Printer spooling
C.Function call management (Recursion)
D.Breadth First Search
Correct Answer: Function call management (Recursion)
Explanation:
The system call stack tracks active subroutines and local variables during recursion.
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36Which of the following is an application of a Queue?
A.Breadth First Search (BFS)
B.Evaluating postfix expressions
C.Checking for balanced parentheses
D.Undo mechanism in text editors
Correct Answer: Breadth First Search (BFS)
Explanation:
BFS uses a queue to explore neighbors level by level.
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37The Peek operation in a Stack:
A.Removes the top element
B.Returns the bottom element
C.Clears the stack
D.Returns the top element without removing it
Correct Answer: Returns the top element without removing it
Explanation:
Peek looks at the Top element but does not modify the stack pointer.
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38In a linked list implementation of a stack, pushing an element requires allocating a new node and:
A.Updating the tail pointer
B.Setting its next pointer to null
C.Setting its next pointer to the current head
D.Traversing to the end of the list
Correct Answer: Setting its next pointer to the current head
Explanation:
The new node becomes the new head (Top), so it must point to the previous head.
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39For a queue implemented with a linked list, if Front == NULL, it means:
A.The queue is empty
B.The queue is full
C.Error condition
D.The queue has one element
Correct Answer: The queue is empty
Explanation:
If the Front pointer is null, there are no nodes in the linked list queue.
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40In the array representation of a circular queue, how do you calculate the next position for Rear?
A.(Rear - 1) % Size
B.Rear - 1
C.Rear + 1
D.(Rear + 1) % Size
Correct Answer: (Rear + 1) % Size
Explanation:
The modulo operator handles the wrap-around from the last index back to index 0.
42What is the result of converting A * (B + C) to postfix?
A.A * B + C
B.A B C + *
C.A B + C *
D.* A + B C
Correct Answer: A B C + *
Explanation:
Inside parentheses B+C becomes BC+. Then A is multiplied by that result: A BC+ *.
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43Which data structure supports the 'undo' feature in text editors?
A.Queue
B.Hash Table
C.Stack
D.Tree
Correct Answer: Stack
Explanation:
Undo operations reverse the most recent action, which fits the LIFO nature of a stack.
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44To reverse a string using a stack, you would:
A.Enqueue all characters, then dequeue
B.Use a priority queue
C.Push all characters, then pop all characters
D.Push half, pop half
Correct Answer: Push all characters, then pop all characters
Explanation:
Pushing ABC results in C at top. Popping yields C, B, A.
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45In a priority queue, if two elements have the same priority, how are they typically processed?
A.FIFO order
B.LIFO order
C.They cannot be processed
D.Randomly
Correct Answer: FIFO order
Explanation:
Standard convention for stable priority queues is to process elements with equal priority in the order they arrived (FIFO).
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46How many stacks are needed to implement a Queue efficiently?
A.1
B.2
C.3
D.4
Correct Answer: 2
Explanation:
Two stacks are required: one for enqueue operations and one to reverse the order for dequeue operations.
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47When transforming an infix expression to postfix, if the scanned operator has lower precedence than the stack top operator:
A.Pop the stack top and print it, then repeat comparison
B.Delete the stack top
C.Push the scanned operator
D.Ignore the scanned operator
Correct Answer: Pop the stack top and print it, then repeat comparison
Explanation:
Higher precedence operators in the stack must be applied first, so they are popped before the lower precedence operator is pushed.
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48In a Deque implemented using a circular array, if Front = 0 and we do deleteFront, what is the new Front?
A.1
B.0
C.-1 (if empty)
D.Size - 1
Correct Answer: 1
Explanation:
Assuming the deque is not empty, deleting from index 0 moves the Front pointer to index 1.
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49Which operation is NOT valid for a standard Stack?
A.Delete Middle
B.Peek
C.Pop
D.Push
Correct Answer: Delete Middle
Explanation:
Standard stacks only allow access and deletion at the Top. Accessing or deleting the middle violates the ADT definition.
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50What is the minimum number of queues needed to implement a Stack?
A.2
B.0
C.3
D.1
Correct Answer: 2
Explanation:
Generally, two queues are used to mimic stack behavior (push/pop) by moving elements back and forth, though it can be done with 1 queue if recursion/call-stack is utilized implicitly.