Find longest subsequence in string
Last updated: September 28, 2025
Quick Overview
Given a string, write a function to find the longest subsequence that can be derived from the string while maintaining the original order of characters. The function should return the length of this longest subsequence. For example, in the string "abcde", the longest subsequence is "abcde" itself, with a length of 5.
Plaid
September 28, 20258
11
3,238 solved
Given a string, write a function to find the longest subsequence that can be derived from the string while maintaining the original order of characters. The function should return the length of this longest subsequence. For example, in the string "abcde", the longest subsequence is "abcde" itself, with a length of 5.
Coding interviews at Plaid 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 in a single pass?
- What is the worst-case input for your solution?
- How would your solution change if the input was sorted?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires us to find the length of the longest subsequence in a given string while maintaining the original order of characters. This can be approached using dynamic programming, which is p...
Approach
- Initialization: Create an array
dpof the same length as the input strings, wheredp[i]will hold the length of the longest subsequence that ends with the character at indexi. Initial...
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