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HashMap / Sliding Window•Pattern: Sliding Window + HashMap•Medium

Longest substring without repeating characters

Problem Intuition & Objective

Find the length of the longest substring with all unique characters.

Time ComplexityO(n)
Optimal
Space ComplexityO(min(n, alphabet))
Memory Bounds
Optimal Algorithmic Approach

Sliding window + HashMap storing last index of each char for O(1) jump.

Core Invariants & Edge Cases

  • Sliding window with a HashSet or character-to-index map
  • When a repeat is found, shrink the window from the left
  • Track max window size throughout
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