MEDIUM NC#18 Sliding Window
567. Permutation in String
📖 Problem
Given two strings s1 and s2, return true if s2 contains a permutation of s1, or false otherwise. In other words, return true if one of s1's permutations is the substring of s2.
🧠 Visual Learning Aid
1 Model the input into the right structure
2 Choose the core technique and invariant
3 Execute step-by-step with a sample
4 Validate complexity and edge cases
JS/TS Refreshers
- •Array methods (`push`, `pop`, `shift`, `slice`)
- •Object/Map/Set usage patterns
- •Function parameter and return typing
- •String/array indexing
- •Set/Map frequency counting
- •Pointer movement invariants
Logical Thinking Concepts
- •Define invariants before coding
- •Check edge cases first (`[]`, single element, duplicates)
- •Estimate time/space before implementation
- •Apply Sliding Window reasoning pattern
💡 Approach
- → Permutation means same characters with same counts
- → Use sliding window of size s1.length on s2
- → Track character counts in current window
- → Expand right and shrink left while maintaining window size
- → Optimize by tracking count of matching characters
- → Time: O(len(s1) + len(s2)), Space: O(26) constant
🛠️ Hints & Pitfalls
Hints
- •Permutation means same characters with same counts
- •Use sliding window of size s1.length on s2
- •Track character counts in current window
Common Pitfalls
- •Expand right and shrink left while maintaining window size
- •Optimize by tracking count of matching characters
- •Time: O(len(s1) + len(s2)), Space: O(26) constant
🧪 Test Cases
Hidden tests on submit: 2
Test Case 1
Not run Input:
checkInclusion('ab', 'eidbaooo'); Expected:
true Test Case 2
Not run Input:
checkInclusion('ab', 'eidboaoo'); Expected:
false Test Case 3
Not run Input:
checkInclusion('adc', 'dcda'); Expected:
true 📝 Code Editor
📤 Output