Find longest subsequence in string
Last updated: March 9, 2026
Quick Overview
Given a string, find the longest subsequence that can be derived from the original string by deleting some characters without changing the order of the remaining characters. The output should be the length of this longest subsequence.
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March 9, 202635
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Given a string, find the longest subsequence that can be derived from the original string by deleting some characters without changing the order of the remaining characters. The output should be the length of this longest subsequence.
Coding interviews at Zoom 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
- What if the input doesn't fit in memory?
- How would you modify your solution to handle streaming input?
- What happens if the input contains duplicates?
- What is the worst-case input for your solution?
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Problem Analysis
To solve the problem of finding the longest subsequence in a string, we can utilize Dynamic Programming (DP). This approach is suitable because we need to build upon previously computed results (s...
Approach
- Initialization: Create an array
dpof the same length as the input strings, wheredp[i]will store the length of the longest subsequence that ends with the characters[i]. Initialize a...
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