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CodingFoundations

Arrays and strings

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Medium

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Arrays & in-place tricksRearranging data without asking for more memory.3 min Hash maps & setsO(1) lookups by turning data into an address.3 min Designing data structuresCombine basic primitives (maps, lists, heaps) to create complex data structures with fast operations.3 min Sliding windowMaintain a flexible constraint over contiguous data by inch-worming your pointers.3 min Stacks & monotonic stacksRemember data in a Last-In, First-Out (LIFO) order to process immediate dependencies.3 min Prefix sums & difference arraysPrecompute cumulative totals to answer range queries instantly.3 min String matching (KMP, Z)Search for a pattern in a text without ever stepping backward.3 min Window functions: running totals, ranks and gapsEach row gets its own little window into the group, and, unlike group by, every row stays on the page.4 min Linked listsData scattered in memory, connected by pointers.3 min Set operationsTwo result sets meet at a junction, and the only real question is which rows survive the meeting.5 min Consistent hashing (key rebalancing)How to add a new server to a distributed database without moving every single piece of data.3 min Consistent hashing and replica setsWalking the ring to ensure data survives a server explosion.3 min Rate limitingA bucket of tokens that quietly refills, spend one per request, and when it runs dry, callers have to wait.4 min Transfer locking and final balanceLocks force concurrent transfers into a safe order, so the books always balance.3 min