Connect Four

Connect Four is the two-player game of dropping coloured discs into a seven-column, six-row board: each disc falls to the lowest free space in its column, and the first player to make a line of four of their colour — across, up and down, or diagonally — wins. If the board fills with no line of four, it is a draw. Play against the computer or with a friend taking turns on the same phone or computer. Against the computer you play red and go first; choose Easy, which looks two moves ahead and sometimes plays loosely, Medium, which looks four ahead, or Hard, which looks seven moves ahead and is difficult to beat. The computer never cheats: it sees the same board you do and chooses its move by searching the possible replies (minimax with alpha-beta pruning), preferring the middle columns, where most lines can be made. Wins in a row against the computer are counted, and your best run is kept on this device. Drop a disc with the arrow buttons above the board, or by clicking a column.

1. Choose the computer (and its strength) or a friend.
2. Drop a disc with a column button, or click the column.
3. Block your opponent’s threes, and build lines that can be finished two ways.
4. Press New game to play again.

• Two-player mode is on one device; there is no online play.
• On Hard, the computer can take a moment on an older phone to choose its move.
• The game, including the computer player, runs in your browser. Nothing is sent anywhere.

Red. Against the computer you are red; with a friend, red starts and you take turns.

Take the middle column early, block every three, and look for a move that makes two threats at once — the opponent can only block one.

With perfect play, the first player can always win by starting in the middle column; it was solved by computer in 1988.

Yes. Tab to the column buttons above the board and press Enter or Space to drop a disc.