I recognized the sliding window pattern pretty quickly, which helped.
First, clarify the problem and edge cases, then propose an efficient sliding window approach that expands and contracts to find the shortest substring containing all distinct characters. Explain the algorithm step-by-step, analyze its time and space complexity, and optionally discuss alternative approaches.
Pro tip: Demonstrate strong problem-solving by discussing trade-offs between approaches and mentioning how you would test the solution with edge cases like empty strings or strings with all unique characters.
Ask clarifying questions to ensure you understand the requirements, such as whether the substring must be contiguous, what to return if no such substring exists, and the expected input size.
Determine the set of distinct characters in the string, as the substring must contain all of them. This can be done by scanning the string once.
Use two pointers to maintain a window that contains all distinct characters. Expand the right pointer to include characters, and once all are included, contract the left pointer to minimize the window length.
Keep track of the minimum window length found during the process, updating it whenever a valid window is found and contracted.
Explain that the time complexity is O(n) since each character is visited at most twice, and space complexity is O(k) where k is the number of distinct characters.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.