Detect permutation in string
Last updated: October 4, 2025
Quick Overview
Given two strings, s1 and s2, determine if any permutation of s1 exists as a substring in s2. The function should return true if such a permutation is found, and false otherwise. The input strings can contain lowercase letters only, and the output should be a boolean value.
JPMorgan
October 4, 202531
14
3,371 solved
Given two strings, s1 and s2, determine if any permutation of s1 exists as a substring in s2. The function should return true if such a permutation is found, and false otherwise. The input strings can contain lowercase letters only, and the output should be a boolean value.
JPMorgan uses this problem in the Technical 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
- How would you parallelize this solution?
- How would your solution change if the input was sorted?
- What happens if the input contains duplicates?
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Practice DSA ProblemsSample Answer
Problem Analysis
To determine if any permutation of string s1 exists as a substring in s2, we realize that the problem can be effectively solved using the sliding window technique along with **frequency counti...
Approach
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Character Count for
s1: First, create a frequency count of the characters ins1. For example, ifs1 = 'abc', the frequency count will be{'a': 1, 'b': 1, 'c': 1}. -
**Sliding Window o...
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