LeetCode Card 330 — Monotonic Stack / Check
Pattern signal
This pattern usually appears when the prompt involves next greater/smaller relationships or range influence determined by nearest boundary violations. Daily Temperatures, Next Greater Element, Trapping Rain Water variants, and histogram area problems are common.
What Check means here
In BASIC, the Check step is where you dry-run the result on edge cases, confirm complexity, and inspect whether the invariant actually held. For Monotonic Stack, that matters because the pattern only becomes useful once the candidate is explicit about what is being tracked, reduced, or preserved.
Interview move
A strong move is to review and stress-test before you hand the answer over. In this pattern family, say out loud what representation makes the problem easier: the map entry, the pointer invariant, the recursion contract, the queue contents, or the DP state. That keeps the implementation attached to a reason.
Common miss
The miss is pushing values instead of the right representation, or not naming the ordering maintained by the stack. BASIC reduces that risk because the stage sequence forces you to earn the implementation instead of jumping straight into it.
BASIC prompt
“Given that this looks like Monotonic Stack, what is the simplest way to dry-run the result on edge cases, confirm complexity, and inspect whether the invariant actually held?”