Detect subsequence in string
Last updated: September 13, 2025
Quick Overview
Given a string and a subsequence, determine if the subsequence can be derived from the string by deleting some characters without changing the order of the remaining characters. Return true if the subsequence exists in the string, and false otherwise.
OpenAI
September 13, 2025105
14
4,100 solved
Given a string and a subsequence, determine if the subsequence can be derived from the string by deleting some characters without changing the order of the remaining characters. Return true if the subsequence exists in the string, and false otherwise.
This coding problem is frequently asked during Phone Screen at OpenAI. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. OpenAI expects candidates to write production-quality code, not just solve the puzzle.
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?
- What happens if the input contains duplicates?
- What is the worst-case input for your solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem at hand requires us to determine if a given subsequence can be derived from a string by deleting some characters without changing the order of the remaining characters. This situation is b...
Approach
- Initialize two pointers: one for the string (
s_ptr) and one for the subsequence (sub_ptr), both starting at index 0. - Iterate through the main string using
s_ptr:- If the character at `...
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