In a Command Pattern implementation that maintains separate stacks for undo and redo operations, what is the average time complexity for performing an undo or redo action?

medium🧠 Conceptual Test Q5 of Q15

OOP & Design Patterns - Command Pattern - Undo/Redo, Request Queuing & Logging

AO(n), because all commands must be re-executed to maintain state

BO(1), since undo and redo involve simple stack push/pop operations

CO(log n), due to searching through command history

DO(n^2), as undo and redo require nested loops over command stacks

Step-by-Step Solution

Solution:

Step 1: Understand the data structures used
Undo and redo stacks are typically implemented as simple stacks (LIFO).
Step 2: Analyze undo/redo operations
Undo pops the last command from the undo stack and pushes it onto the redo stack, and vice versa for redo.
Final Answer:
Option B -> Option B
Quick Check:
Stack push/pop operations are constant time [OK]

Quick Trick: Undo/redo stacks use push/pop, so operations are O(1) [OK]

Common Mistakes:

MISTAKES

Assuming undo requires re-executing all commands
Confusing time complexity with space complexity
Thinking redo requires searching through history

Trap Explanation:

PITFALL

Option B looks plausible if one thinks undo requires replaying commands, but stacks avoid this.

Interviewer Note:

CONTEXT

Tests understanding of time complexity in undo/redo stack operations.

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In a Command Pattern implementation that maintains separate stacks for undo and redo operations, what is the average time complexity for performing an undo or redo action?

Step 1: Understand the data structures used

Step 2: Analyze undo/redo operations

Final Answer:

Quick Check:

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