LeetCode Card 338 — Bit Manipulation / Structure
Pattern signal
This pattern usually appears when the prompt involves parity, masks, compact state, powers of two, or toggling flags efficiently. Single Number, counting bits, subset masks, and low-level state operations sit here.
What Structure means here
In BASIC, the Structure step is where you state the invariant, helper contract, or control-flow skeleton before coding. For Bit Manipulation, 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 make the plan visible before full execution. 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 using bit tricks as memorized magic without understanding what each mask encodes. 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 Bit Manipulation, what is the simplest way to state the invariant, helper contract, or control-flow skeleton before coding?”