Tide

Goal

On a beach seen from above, little crabs must reach their burrow before the tide carries them away. You help them by changing the beach, one action at a time. The beach is won when every crab is home.

How a turn works

• You take one action: push a rock one square (tap it then an arrow, or drag it), lay a plank on the water, dig a channel, drift a floating bridge, or simply wait.
• The crabs move one square toward their burrow along the shortest free path. The rule never changes: the small ghost arrows show each crab’s next step and the dots show the rest of its path. On a tie, a crab prefers north, then east, south and west.
• The sea rises one notch (two during the spring tide). Every sand square shows its height; dark, wet sand will be reached by the next wave.
• A crab that ends up in the water shows a red bubble: it has one turn to get out, otherwise the next wave sweeps it away. A crab on a plank stays dry.

The pieces

• Grey rocks: they can be pushed one square onto a free square (sand or water, with no crab or plank).
• Green rocks, covered in seaweed: they slide until the next obstacle.
• Planks: laid on a water square, they make a safe bridge. How many you have is shown on the button.
• Channels: digging a sand square lowers it to sea level, which cuts a path and forces the crabs to go around.
• Floating bridges: resting on the water, they drift one square onto another water square when pushed.
• Cliffs and grassy dunes are never covered.

Stars

Waiting is free: only real actions count. Every beach has a target: the smallest possible number of actions, computed by a solver. Hit the target for three stars, go up to two over it for two, any more earns one. Using a hint caps you at two.

Modes

• Solo: the campaign of five worlds (Quiet Bay, Slippery Rocks, Salt Marsh, Spring Tide, Reef) of nine or ten beaches each, unlocked in turn (six beaches cleared open the next world); the beach of the day, the same for everyone; and generated beaches at five difficulties. Unlimited undo, hints and instant restart.
• Against the AI: you and the AI each solve your own copy of the same beach; its progress is shown in a thumbnail. Fewest actions wins, then fastest. Five AI levels, from absent-minded to razor sharp.
• Two players: a crab duel on the same beach, taking turns. Player 1 guides the orange crabs, player 2 the blue crabs, but every action changes the beach for both. Most crabs home wins, then fewest actions.
• Online: a race on the same beach, fewest actions in total wins.

Controls

With a finger or the mouse: tap a rock, then an arrow, or drag the rock. With the keyboard: arrows move the cursor, Space selects, then an arrow pushes; E to wait, P for a plank, G for a channel, U to undo, H for a hint, R to restart, L for the map.

About the solver

Each beach is verified by a two-cost breadth-first search (waiting is free, an action costs one) over the full state of the beach. It computes the target, gives the hints, guarantees the generated beaches and guides the AI.