Got the sliding window approach down fine, used a hash set to track what's in the current window and moved the left pointer when I hit a duplicate.
Start by clarifying the problem and edge cases, then present a sliding window solution using a hash map to track character indices, achieving O(n) time. Discuss optimization by using a fixed-size array for ASCII characters to reduce constant factors and memory overhead.
Pro tip: Mention that the sliding window approach is optimal in time complexity, but for Boeing's embedded or real-time systems, optimizing space and constant factors (e.g., using a 128-element array) can be critical. Also, briefly note that if the character set is large (e.g., Unicode), a hash map is more appropriate.
Ask about the character set (ASCII, Unicode), input size, and whether the substring must be contiguous. Confirm that we need the length, not the substring itself.
Mention that a brute force approach checks all substrings, which is O(n^3) or O(n^2) with optimization, and is impractical for large inputs.
Explain the two-pointer technique: expand right pointer, and when a duplicate is found, move left pointer to the right of the previous occurrence. Use a hash map to store the last index of each character.
State that the algorithm runs in O(n) time and O(min(n, m)) space, where m is the size of the character set. Emphasize that each character is visited at most twice.
Propose replacing the hash map with a fixed-size array (e.g., 128 or 256 for ASCII) to reduce overhead. For Unicode, suggest using a hash map but note that the alphabet size is large. Also, mention that the left pointer can jump directly to the stored index + 1.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.