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Best Time to Buy and Sell Stock
Best Time to Buy and Sell Stock is the sliding window pattern: grow, shrink, and maintain just enough state to stay linear. It's a great warm-up that builds stateful scanning without a ton of moving parts. The trap is updating window state in the wrong order when you expand or shrink.
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Sliding Window Algorithm
Sliding window processes arrays or strings by moving a window through the data, updating results incrementally instead of recalculating from scratch. Reach for it when you see "contiguous subarray," "longest/shortest substring," or "at most K distinct."
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