Detect permutation in string
Last updated: April 1, 2026
Quick Overview
Given two strings, s1 and s2, determine if s2 contains any permutation of s1 as a substring. You should return true if such a permutation exists, and false otherwise. The solution should efficiently handle the input strings, considering their lengths and character distributions.
Expedia
April 1, 202628
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Given two strings, s1 and s2, determine if s2 contains any permutation of s1 as a substring. You should return true if such a permutation exists, and false otherwise. The solution should efficiently handle the input strings, considering their lengths and character distributions.
Coding interviews at Expedia 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
- Can you solve this in a single pass?
- How would your solution change if the input was sorted?
- What is the worst-case input for your solution?
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Problem Analysis
To determine if string s2 contains any permutation of string s1, we can leverage the concept of character frequency. A permutation of s1 will have the same character counts as s1. This suggest...
Approach
- Character Count: First, create a frequency count of characters in
s1. For example, fors1 = 'abc', the frequency count would be{ 'a': 1, 'b': 1, 'c': 1 }. - Sliding Window: Initiali...
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