Detect subsequence in array
Last updated: June 7, 2026
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: true if the subsequence exists in the array, and false otherwise.
DoorDash
June 7, 202616
5
4,669 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: true if the subsequence exists in the array, and false otherwise.
This coding problem is frequently asked during Onsite at DoorDash. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. DoorDash 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
- Can you solve this in a single pass?
- How would your solution change if the input was sorted?
- How would you test this solution thoroughly?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires us to determine if a given subsequence exists within an array of integers in the same order. This can be effectively solved using the two-pointer technique. The reason this te...
Approach
- Initialize two pointers:
ifor the array andjfor the subsequence, both set to 0. - Loop through the array using the pointer
i:- If the current element in the array (arr[i]) matches the...
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