LeetCode Card 235 — Binary Search / Check
Pattern signal
This pattern usually appears when the prompt involves sorted structure or hidden monotonic predicate. Search Insert Position, Search in Rotated Sorted Array, first/last occurrence, and answer-space search all fit.
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 Binary Search, 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 defining the midpoint but not the invariant about where the answer still lives. 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 Binary Search, what is the simplest way to dry-run the result on edge cases, confirm complexity, and inspect whether the invariant actually held?”