Detect subsequence in array
Last updated: October 11, 2025
Quick Overview
Given an array of integers and a subsequence, determine if the subsequence can be found within the array in the same order, but not necessarily consecutively. The function should return a boolean value indicating whether the subsequence exists in the array. For example, given the array [1, 2, 3, 4, 5] and the subsequence [2, 4], the output should be true.
Datadog
October 11, 20253
13
1,171 solved
Given an array of integers and a subsequence, determine if the subsequence can be found within the array in the same order, but not necessarily consecutively. The function should return a boolean value indicating whether the subsequence exists in the array. For example, given the array [1, 2, 3, 4, 5] and the subsequence [2, 4], the output should be true.
Datadog uses this problem in the Phone Screen 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
- 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 optimize the space complexity of your solution?
- How would you test this solution thoroughly?
- What happens if the input contains duplicates?
- How would you parallelize this solution?
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Problem Analysis
The problem requires us to determine if a given subsequence can be found within an array in the same order, though not necessarily consecutively. This is a classic use case for the **two-pointer techn...
Approach
- Initialize two pointers:
ifor the array andjfor the subsequence, both starting at 0. - Iterate through the array using the pointer
i:- If the current element in the array (
array[i])...
- If the current element in the array (
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