Explain minimum window substring sliding window approach
Reported in HelloFresh European engineering loops. Advanced string window question seen in strong coding interviews.
Interview scenario
Context for HelloFresh candidates:
Given strings s and t, find the smallest window in s containing all chars of t.
Model answer
Try answering aloud first
Cover trade-offs, structure, and a concrete example before revealing the baseline response.
How to frame this at HelloFresh: Connect your answer to measurable impact, clarity of thought, and trade-offs the team cares about. Below is a strong baseline response you can adapt with your own project examples.
Use a sliding window with frequency maps. Expand the right pointer to satisfy required character counts, then contract from the left while the window remains valid to minimize length.
Track two counters: total required unique characters and currently satisfied unique characters. This avoids recomputing full map matches at each step and keeps complexity near O(n).
In explanation, highlight that repeated letters in t matter, so counts are compared by frequency, not just set membership.
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