dsa1 min read
Minimum Consecutive Cards to Pick Up [Medium] — HashMap Window
Find the minimum number of consecutive cards that contain a matching pair using a HashMap tracking last seen positions.
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Count Subarrays with Score Less Than K [Hard] — Shrinkable Window
Count subarrays where score = sum × length is less than k using a shrinkable sliding window with running sum.
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Minimum Window Substring [Hard] — have/need Frequency Counter
Find the smallest window in s containing all characters of t using a have/need counter to track when the window is valid.
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Sliding Window Maximum [Hard] — Monotonic Decreasing Deque
Find the maximum in every sliding window of size k in O(n) using a monotonic decreasing deque of indices.
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Shortest Subarray with Sum ≥ K [Hard] — Monotonic Deque on Prefix
Find the shortest subarray with sum >= k, handling negative numbers correctly using a monotonic deque on prefix sums.
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