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The Stack That Stays Sorted
Recognize next-greater and next-smaller questions and see why one sorted stack answers them all in a single pass.
Multiple choiceTap - 2
Next Greater Element
Scan once with a stack of unresolved indices — every pop hands a waiting element its answer.
Complete codeMultiple choiceTrace - 3
Final Prices with Discount
Flip the comparison: the same one-pass stack scan finds each item's discount the moment a smaller-or-equal price arrives.
Complete codeMultiple choice - 4
Daily Temperatures
Stack the indices of unresolved days — a warmer day pops them, and the answer is the index distance.
Complete codeMultiple choiceTrace - 5
Online Stock Span
Previous-greater on a stream: pop the prices you dominate and absorb their spans — never recount.
Complete codeMultiple choiceTrace - 6
Remove K Digits
Keep the kept digits climbing — while removals remain, pop any bigger digit the newcomer beats, then trim the tail and strip leading zeros.
Complete codeMultiple choiceTrace - 7
Monotonic Stack CheckpointCheckpoint
No new concepts — the island's pop-to-resolve rules under pressure: choosing the stack direction, tracing pops, the while condition, a duplicate-handling bug, and why one pass really is O(n).
DebugFill blankMultiple choiceTrace - 8
Monotonic Stack ReviewReview
Mixed recap of the island: spotting stack problems, pop mechanics, price discounts, greedy digit removal, spans, and what one-pass stacks really cost.
Complete codeDebugMultiple choiceTapTrace - 9
Boss: Largest RectangleBoss
The monotonic-stack finale: an increasing index stack hands every bar its previous-smaller and next-smaller walls at pop time, and a sentinel 0 flushes the survivors.
Complete codeDebugCode orderMultiple choiceTrace
Search & Priority Patterns is part of AlgoFox Pro
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