Isolate

📖 Strategy guide: How to beat the Isolate bot: exits, regions and the Hard search

How to play

This is our version of the isolation game that has been played on paper and on boards since the 1970s. On a board of 7×7 tiles your pawn, the penguin in the blue hat, starts in the middle of the bottom edge, the computer's crested penguin opposite, and you move first.

Every turn has two steps. First move your pawn one step in any of the eight directions, onto a tile that is still there and is not under the other pawn. Then remove any one free tile, anywhere on the board, even the one you just left or one next to your own pawn; it is gone for the rest of the game. The sea turns darker while a removal is due. Whoever cannot move at the start of their turn loses, so there are no draws. ↶ takes back your last turn and the computer's reply, after a loss too.

Levels

Easy steps to a tile with some room around it and usually removes a random tile next to your pawn; it does not plan. Normal looks two full turns ahead: its own turn and your best answer. Hard looks further: usually three turns, more as the board empties, and to the very end in the last few moves. A win scores 10, 20 or 30 points on the leaderboard, by level.

How the computer plays

Normal and Hard run a minimax search with alpha-beta pruning over whole turns, a move plus a removal. Checking every removal would be too slow, so the search only tries tiles within two steps of the other pawn and tiles that would cut that pawn's part of the board in two. Hard deepens the search one turn at a time until it has spent its budget, about a third of a second at most.

Positions at the end of the search are scored by territory, the tiles a pawn can reach before the other one, plus the number of moves each pawn has right now. When the pawns can no longer reach each other, the computer counts the tiles in each region: the bigger one outlasts the smaller.

Tips

• Early on, room matters more than position: step to tiles with many free neighbours and stay off the edges.
• Remove tiles next to the computer's pawn, not next to your own. Every hole beside you is one exit fewer.
• If a row of holes can split the board, finish the wall only when your side is the bigger one.
• Do not walk into corners or dead ends: a corner has only three exits.