Data Structures Stacks and Queues

Question 1

Which real-world scenario best illustrates LIFO (Last In, First Out) behavior?

Accepted Answer

Undo/redo functionality in a text editor

Answer

Waiting in a checkout line

Answer

Scheduling print jobs on a printer

Answer

Breadth-first traversal of a graph

Question 2

What is the time complexity of the push and pop operations on a stack?

Accepted Answer

O(1) for both

Answer

O(n) for both

Answer

O(log n) for both

Answer

O(1) push, O(n) pop

Question 3

How can a queue be implemented using two stacks with amortized O(1) enqueue and dequeue?

Accepted Answer

Enqueue to stack1; dequeue pops from stack2, transferring from stack1 when stack2 is empty

Answer

Use one stack for each direction and alternate operations

Answer

Always reverse one stack after each operation

Answer

Store elements sorted across both stacks

Question 4

What is a monotonic stack used for?

Accepted Answer

Maintaining elements in strictly increasing or decreasing order to solve next-greater-element problems

Answer

Implementing a priority queue

Answer

Balancing parentheses in expressions

Answer

Evaluating postfix expressions

Question 5

Which algorithm uses a stack to evaluate postfix (Reverse Polish Notation) expressions?

Accepted Answer

Push numbers, pop two operands when an operator is found, push result

Answer

Use two stacks: one for numbers, one for operators

Answer

Convert to infix first then evaluate

Answer

Recursively evaluate each operator

Question 6

What is the main advantage of a circular queue over a linear array-based queue?

Accepted Answer

Reuses freed space at the front without shifting elements

Answer

Faster enqueue time

Answer

Supports priority ordering

Answer

Eliminates the need for a size variable