LeetCode Card 343 — Matrix Traversal / Structure
Pattern signal
This pattern usually appears when the prompt involves grid movement, boundary control, in-place marking, or BFS/DFS over 2D structure. Spiral Matrix, Set Matrix Zeroes, Number of Islands, and flood-fill style problems commonly appear.
What Structure means here
In BASIC, the Structure step is where you state the invariant, helper contract, or control-flow skeleton before coding. For Matrix Traversal, 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
Candidates lose track of boundary checks or mutate cells without planning how state will be preserved. 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 Matrix Traversal, what is the simplest way to state the invariant, helper contract, or control-flow skeleton before coding?”