Detect permutation in string
Last updated: October 31, 2025
Quick Overview
Given two strings, determine if one string is a permutation of the other. The input consists of two strings, and the output should be a boolean value indicating whether the second string can be formed by rearranging the characters of the first string. Consider case sensitivity and ignore spaces in the strings.
ServiceNow
October 31, 20251
15
245 solved
Given two strings, determine if one string is a permutation of the other. The input consists of two strings, and the output should be a boolean value indicating whether the second string can be formed by rearranging the characters of the first string. Consider case sensitivity and ignore spaces in the strings.
This coding problem is frequently asked during Onsite at ServiceNow. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. ServiceNow expects candidates to write production-quality code, not just solve the puzzle.
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 test this solution thoroughly?
- Can you solve this iteratively instead of recursively (or vice versa)?
- What happens if the input contains duplicates?
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Practice DSA ProblemsSample Answer
Problem Analysis
To determine if one string is a permutation of another, we can utilize the concept of frequency counting. The two strings must contain the exact same characters with the same frequency — a characteris...
Approach
- Sanitize Input: First, we need to ignore spaces in both strings. This can be done by replacing spaces or filtering them out.
- Check Lengths: If the lengths of the two sanitized strings ar...
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