Find longest subsequence in array
Last updated: December 30, 2025
Quick Overview
Given an array of integers, find the longest subsequence that can be derived from the array, where the elements of the subsequence are in increasing order. The function should return the length of this longest increasing subsequence.
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December 30, 2025131
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Given an array of integers, find the longest subsequence that can be derived from the array, where the elements of the subsequence are in increasing order. The function should return the length of this longest increasing subsequence.
Snapchat 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
- 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
- How would your solution change if the input was sorted?
- How would you modify your solution to handle streaming input?
- Can you solve this in a single pass?
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Practice DSA ProblemsSample Answer
Problem Analysis
To find the longest increasing subsequence (LIS) in an array of integers, we can utilize the dynamic programming approach combined with binary search for optimal performance. The key pattern here is t...
Approach
- Initialization: Start by creating an empty list
dpthat will store the smallest tail of all increasing subsequences found. - Iterate through the array: For each element in the input arra...
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