Implement Stack with O(n) time
Last updated: March 29, 2026
Quick Overview
Implement a stack data structure that supports push, pop, and peek operations, ensuring that all operations run in O(n) time complexity. Your implementation should include methods to add an element to the top of the stack, remove the top element, and retrieve the top element without removing it. The stack should handle edge cases such as underflow when popping from an empty stack.
Goldman Sachs
March 29, 202624
15
4,841 solved
Implement a stack data structure that supports push, pop, and peek operations, ensuring that all operations run in O(n) time complexity. Your implementation should include methods to add an element to the top of the stack, remove the top element, and retrieve the top element without removing it. The stack should handle edge cases such as underflow when popping from an empty stack.
Goldman Sachs uses this problem in the Phone Screen to evaluate your algorithmic thinking. They expect you to discuss multiple approaches, analyze trade-offs between them, and implement the optimal solution with clean, readable code.
What the Interviewer Expects
- Recognize the underlying problem pattern (sliding window, two pointers, BFS/DFS, etc.)
- Discuss multiple approaches and trade-offs before coding
- Implement an optimal solution with clean, production-quality code
- Handle all edge cases including boundary conditions and invalid input
- Optimize both time and space complexity with clear justification
- Test your solution systematically with well-chosen examples
Key Topics to Cover
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- How would your solution change if the input was sorted?
- Can you solve this in a single pass?
- What happens if the input contains duplicates?
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Practice DSA ProblemsSample Answer
Problem Analysis
To implement a stack with O(n) time complexity for all operations (push, pop, and peek), we need to carefully consider how we manage the underlying data structure. The pattern that applies here is usi...
Approach
- Initialization: Start with an empty list to represent the stack.
- Push: To add an element, append it to the end of the list. However, to maintain O(n) time complexity, we will shift all...
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