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Sliding Window•Pattern: Fixed Sliding Window•Medium

Permutation in string (sliding window)

Problem Intuition & Objective

Check if any permutation of pattern p exists as a substring of string s.

Time ComplexityO(|s|)
Optimal
Space ComplexityO(1) (26 chars)
Memory Bounds
Optimal Algorithmic Approach

Fixed sliding window with frequency diff tracking.

Core Invariants & Edge Cases

  • Fixed-size window of len(p) over s
  • Compare character frequency maps
  • Use a 'diff' counter to avoid full-array comparison each slide
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