Implement Hash Map with in-place
Last updated: February 28, 2026
Quick Overview
Implement a hash map data structure that supports in-place get and put operations, allowing for average O(1) time complexity for both operations. Your implementation should handle collisions using chaining or open addressing and must support dynamic resizing as needed. The input will consist of key-value pairs for insertion, and the output should be the value associated with a given key during retrieval.
ServiceNow
February 28, 202620
3
1,150 solved
Implement a hash map data structure that supports in-place get and put operations, allowing for average O(1) time complexity for both operations. Your implementation should handle collisions using chaining or open addressing and must support dynamic resizing as needed. The input will consist of key-value pairs for insertion, and the output should be the value associated with a given key during retrieval.
Coding interviews at ServiceNow focus on problem-solving approach as much as the final solution. The interviewer wants to see you break down the problem, consider edge cases, and optimize iteratively. Communication throughout the process is key.
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
- Can you solve this iteratively instead of recursively (or vice versa)?
- Can you solve this in a single pass?
- What if the input doesn't fit in memory?
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Practice DSA ProblemsSample Answer
Problem Analysis
To solve this problem, we need to implement a hash map which allows for efficient O(1) average time complexity for both 'put' and 'get' operations. The pattern that applies here is the hash table stru...
Approach
- Initialization: Start with an initial array size (e.g., 8) and a threshold for resizing (e.g., 0.75).
- Hash Function: Implement a simple hash function that computes the index based on th...
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