Find longest subsequence in array
Last updated: May 12, 2026
Quick Overview
Given an array of integers, find the longest subsequence such that all elements of the subsequence are sorted in non-decreasing order. The function should return the length of this longest subsequence. The input will be an array of integers, and the output should be a single integer representing the length of the longest subsequence.
Twitter/X
May 12, 20262
3
3,048 solved
Given an array of integers, find the longest subsequence such that all elements of the subsequence are sorted in non-decreasing order. The function should return the length of this longest subsequence. The input will be an array of integers, and the output should be a single integer representing the length of the longest subsequence.
Coding interviews at Twitter/X focus on problem-solving approach as much as the final solution. The interviewer wants to see you break down the problem, consider edge cases, and optimize iteratively. Communication throughout the process is key.
What the Interviewer Expects
- Quickly identify the optimal approach and its theoretical basis
- Handle complex algorithm design with multiple interacting components
- Write concise, elegant code under time pressure
- Prove correctness of your approach and discuss alternative solutions
- Optimize beyond the obvious: discuss constant factor improvements
- Address follow-up variations and explain how the solution generalizes
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 you modify your solution to handle streaming input?
- How would you test this solution thoroughly?
- Can you solve this in a single pass?
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Problem Analysis
To solve the problem of finding the longest subsequence in an array of integers that is sorted in non-decreasing order, we can utilize a dynamic programming approach, which is well-suited for problems...
Approach
- Initialize an array
dpof the same length as the input arraynums, where each element is set to 1, since the minimum length of a subsequence can be 1 (the element itself). - Iterate through ...
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