Detect subsequence in string
Last updated: September 20, 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.
Datadog
September 20, 2025215
9
1,809 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.
This coding problem is frequently asked during Onsite at Datadog. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Datadog expects candidates to write production-quality code, not just solve the puzzle.
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 iteratively instead of recursively (or vice versa)?
- Can you optimize the space complexity of your solution?
- Can you solve this in a single pass?
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Practice DSA ProblemsSample Answer
Problem Analysis
To determine if a given subsequence exists within a string, we can utilize a two-pointer technique. This is ideal here because we want to traverse both the string and the subsequence simultaneously, c...
Approach
- Initialize two pointers: one (
i) for the main string and another (j) for the subsequence. - Loop through the main string until either pointer reaches the end.
- Whenever characters at `stri...
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