How to play Connect Four
- Choose a mode: computer (easy), computer (hard) or two players on one device. You play blue and move first in the opening round; the starting player alternates each round.
- Click or tap a column to drop a disc, or use the left and right arrow keys and press Enter. Keys 1 to 7 drop directly into a column.
- Discs fall to the lowest empty cell. The first player with four connected discs wins; a full board is a draw.
- The score panel counts wins and draws for this session. Reset clears it.
Tips
- Take the centre column early: more winning lines pass through it than through any other column.
- Count threats in pairs. Two threats stacked in the same column (odd and even rows) are usually decisive.
- Before dropping a disc, look at the cell above it. Filling a column can hand your opponent the winning square directly on top.
- The hard computer looks four moves ahead. Beat it by building slow diagonal threats it is forced to block one at a time.
About Connect Four
Connect Four was published by Milton Bradley in 1974. It was solved in 1988 by James Allen and Victor Allis: with perfect play the first player always wins by starting in the centre column. Human games are far from perfect, which is what keeps it fun.
The hard computer here uses a minimax search with alpha-beta pruning and a positional evaluation; the easy computer only blocks obvious wins and otherwise plays at random.
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