Detect subsequence in string
Last updated: November 22, 2025
Quick Overview
Given a string and a subsequence, determine if the subsequence can be found within the string in the same order, but not necessarily consecutively. Return true if the subsequence exists in the string, and false otherwise. For example, given the string "abcde" and the subsequence "ace", the output should be true.
xAI
November 22, 202524
5
123 solved
Given a string and a subsequence, determine if the subsequence can be found within the string in the same order, but not necessarily consecutively. Return true if the subsequence exists in the string, and false otherwise. For example, given the string "abcde" and the subsequence "ace", the output should be true.
xAI uses this problem in the Take-home Project 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
- Identify the correct data structure and algorithm for the problem
- Write clean, bug-free code with proper variable naming
- Analyze time and space complexity correctly
- Handle basic edge cases (empty input, single element)
- Communicate your thought process while coding
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 you modify your solution to handle streaming input?
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Practice DSA ProblemsSample Answer
Problem Analysis
To determine if a subsequence exists within a given string, we can utilize a two-pointer technique. The main observation is that while we traverse through the main string, we can maintain a pointer fo...
Approach
- Initialize two pointers:
ifor the main string andjfor the subsequence, both starting at 0. - Iterate through the main string using the pointer
i. For each character in the main string: ...
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