Two Pointers on string
Last updated: May 30, 2026
Quick Overview
Given a string, implement the two pointers technique to find the longest substring without repeating characters. Your function should return the length of this substring. The input will be a single string, and the output should be an integer representing the maximum length of the substring found.
TikTok
May 30, 2026145
3
285 solved
Given a string, implement the two pointers technique to find the longest substring without repeating characters. Your function should return the length of this substring. The input will be a single string, and the output should be an integer representing the maximum length of the substring found.
TikTok uses this problem in the Take-home Project 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
- What is the worst-case input for your solution?
- How would you test this solution thoroughly?
- What happens if the input contains duplicates?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires us to find the longest substring without repeating characters in a given string. The two pointers technique is applicable here as it allows us to dynamically adjust our search win...
Approach
- Initialize two pointers:
startat 0 andendat 0. This will denote the current window of characters being considered. - Use a hash set
seento store characters in the current window. - It...
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