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Monotonic Stack Interview Questions

Keep the stack increasing or decreasing, and popping becomes the moment you have found an element's next greater or smaller neighbour - the whole scan stays O(n). It is the standard answer to daily-temperatures, largest-rectangle-in-histogram, and trapping-rain-water. Genuinely hard to invent under interview pressure, which is exactly why it is worth recognising cold.

Recognise it when you see

"Next greater/smaller element", or a maximum rectangle/area over a histogram.

7 problems. Each one runs in an in-browser editor against real test cases, with hints and a worked solution.

Medium1

Daily TemperaturesPremium

Medium

Hard6

Trapping Rain WaterPremium

HardTwo PointersDynamic Programming

Largest Rectangle in HistogramPremium

Hard

Maximal RectanglePremium

HardDynamic ProgrammingMatrix

Sliding Window MaximumPremium

HardSliding Window

Sliding Window Maximum (Monotonic Deque)Premium

HardSliding Window

Largest Rectangle in Histogram (Monotonic Stack)Premium

Hard

Learn the triggers, not just the templates

The patterns cheat sheet covers all of these in one page - what each one looks like in a problem statement, and the template that follows.

Interview patterns cheat sheet Big-O cheat sheet All coding problems

Monotonic Stack Interview Questions

Keep the stack increasing or decreasing, and popping becomes the moment you have found an element's next greater or smaller neighbour - the whole scan stays O(n). It is the standard answer to daily-temperatures, largest-rectangle-in-histogram, and trapping-rain-water. Genuinely hard to invent under interview pressure, which is exactly why it is worth recognising cold.