Implement Stack with O(1) space
Last updated: August 4, 2025
Quick Overview
Implement a stack data structure that supports push, pop, and top operations, all while using O(1) space complexity. Your implementation should allow for the following operations: `push(value)`, which adds an element to the top of the stack; `pop()`, which removes the top element and returns it; and `top()`, which returns the top element without removing it. Ensure that your stack can handle a sequence of these operations efficiently.
Anduril
August 4, 202540
7
257 solved
Implement a stack data structure that supports push, pop, and top operations, all while using O(1) space complexity. Your implementation should allow for the following operations: `push(value)`, which adds an element to the top of the stack; `pop()`, which removes the top element and returns it; and `top()`, which returns the top element without removing it. Ensure that your stack can handle a sequence of these operations efficiently.
Anduril uses this problem in the Technical 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 you test this solution thoroughly?
- How would you parallelize this solution?
- What happens if the input contains duplicates?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires implementing a stack with O(1) space complexity. The key challenge here is to maintain the properties of a stack (LIFO - Last In, First Out) while using constant space. The operat...
Approach
- Node Structure: Create a Node class that will hold the value and a pointer to the next node.
- Stack Operations:
- Push: Create a new node with the given value and link it to th...
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