LeetCode Card 254 — Fast and Slow Pointers / Implement
Pattern signal
This pattern usually appears when the prompt involves cycle detection, midpoint discovery, or relative-speed traversal. Linked List Cycle, Palindrome Linked List, and finding list middles are canonical examples.
What Implement means here
In BASIC, the Implement step is where you write the code in the same order as the chosen skeleton so the logic stays stable. For Fast and Slow Pointers, 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 transcribe the plan instead of improvising. 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 know the trick but cannot explain why the pointer speeds produce the desired meeting or split. 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 Fast and Slow Pointers, what is the simplest way to write the code in the same order as the chosen skeleton so the logic stays stable?”