Connect 4

Take turns dropping discs into the 7 columns. The first player to line up four of their own discs across, down or diagonally wins. You play red and move first; the hard computer looks six moves ahead.

How to play Connect 4

1. Click a column to drop a disc; it falls to the lowest empty space.
2. Players alternate. Four in a row (horizontal, vertical or diagonal) wins.
3. If all 42 spaces fill with no line, the game is a draw.

Strategy

• Control the center column: more lines of four pass through it than any other.
• Block three-in-a-rows before they become four.
• Build two threats at once so your opponent can stop only one.
• Think about which spaces become playable after each move.

The math behind it

The board has 7 × 6 = 42 spaces and 69 possible winning lines. In 1988 the game was solved: with perfect play the first player can always win by starting in the center. The computer here uses minimax with alpha-beta pruning to skip moves that cannot change the result.

Connect 4 quiz: 10 questions

Test yourself with 10 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.

Frequently asked questions

Can I beat the hard computer?

Yes, but it looks 6 moves ahead, so plan double threats.

Who goes first?

Red (you) goes first against the computer.

Can two people play?

Yes. Choose Two players and take turns on one device.

Is Connect 4 solved?

Yes. The first player wins with perfect play starting in the center.

Does it work on phones?

Yes. Tap a column.

Sources

• Wikipedia: Connect Four (mathematical solution)

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