How should I practice Transform L/R Pieces on a Circular Board?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Google phone screen and onsite interview problems in FastPrep.

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Transform L/R Pieces on a Circular Board

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Problem statement

start and target describe boards of equal length. Each cell is 'L', 'R', or '.'.

An 'L' piece moves only left.
An 'R' piece moves only right.
A piece may move any positive distance through empty cells, but it may not pass through or land on another piece.
Pieces may move in any order.

If circular is false, pieces cannot leave the board. If circular is true, the board wraps: moving left from index 0 continues at index n - 1, and moving right from index n - 1 continues at index 0.

Return whether start can be transformed into target.

Function

canTransformLRPieces(start: String, target: String, circular: boolean) → boolean

Examples

Example 1

start = ".L..R..R."target = "L......RR"circular = falsereturn = true

The nonempty piece order is unchanged. L moves from 1 to 0, while the two R pieces move from 4 and 7 to 7 and 8.

Example 2

start = "L.."target = "..L"circular = truereturn = true

The L piece leaves index 0 through the left boundary and re-enters at index 2.

Example 3

start = "RL.."target = "LR.."circular = truereturn = false

Each piece is immediately blocked in its allowed direction. Reaching the target would require the two pieces to cross.

Constraints

1 <= start.length == target.length <= 3000.
Both strings contain only 'L', 'R', and '.'.