Battleship Game Engine · Approach

01 · Develop the design

Plan the design

Use an explicit placement/play/finished state machine, validated fleet geometry and unique shot records. A scoped view layer exposes public results without returning the opponent’s hidden board.

Stage 1

Declare the variant rules

Choose board dimensions, required ship lengths and whether ships may touch. This exercise allows touching but rejects overlap and diagonal/bent placement.

Stage 2

Validate before committing a shot

Check PLAYING phase, current player, bounds and prior shots first. Only a valid shot updates hit state and advances the turn.

Stage 3

Separate internal and player state

The engine knows both fleets. A ViewPolicy returns a filtered immutable snapshot for one player or spectator.

02 · Work through the method

Step-by-step approach

Configure board dimensions and the required fleet lengths. Validate each ship as in-bounds, straight, contiguous and nonoverlapping; touching is permitted under this exercise’s rules.
Lock fleet placement once both complete fleets are ready and transition to PLAYING with a defined first player. Internal ship/cell identities are immutable after this point.
A shot validates phase, actor, bounds and uniqueness before mutation. Record miss/hit, mark a ship sunk only when all its distinct cells have been hit, and win when every opponent ship is sunk.
Advance to the other player after every valid nonterminal shot under this variant. Invalid shots change nothing. ViewPolicy reveals own fleet and opponent shot knowledge only; terminal state rejects further shots.

03 · Justify the choices

Why this approach works

What should an opponent view reveal?

Only information allowed by the view policy, such as observed shots/results

Domain snapshots must enforce hidden-information boundaries rather than rely on UI concealment.

What does a repeated shot do?

Return an invalid-move result without mutating state

Shot identity and validation prevent duplicated hits or accidental turn changes.

When may play begin?

After both complete fleets pass placement rules

The game phase transition must enforce fleet completeness independently of the UI.

04 · Plan the evidence

Validation strategy

Bent, overlapping, incomplete and out-of-bounds fleets are rejected.
Repeated/wrong-player shots preserve state and turn.
A ship sinks only after all distinct cells are hit.
Opponent snapshots never expose unrevealed cells and terminal games accept no further shot.

Trade-offs to explain

Rules such as extra turns on hits or no-touch placement are variants and must be explicitly configured.
Hidden information requires server-side enforcement for network play; client-side filtering alone is insufficient.
A pure engine is easy to test; online command versions and persistence are separate adapters.