Four Across

Four Across is a two-player disc-drop strategy game on a 7-column, 6-row grid. You play as red. The AI plays as gold. Each turn, click a column to drop a disc. It falls to the lowest open row in that column. The first player to connect four discs in a row, horizontally, vertically, or diagonally, wins. If all 42 positions fill without a winner, it's a draw.

Three difficulty levels control how far ahead the AI thinks. Easy searches 3 moves, Medium searches 5, and Hard searches 7. On Hard, the AI uses minimax with alpha-beta pruning, center-column preference, and weighted evaluation of all directions. It checks for immediate wins and immediate blocks before entering the full tree search. It won't miss an obvious one-move win or an obvious trap. The AI values blocking more heavily than attacking. It penalizes a player threat of three-in-a-row with an open fourth at negative 120 versus its own equivalent offensive position at positive 50.

Discs animate downward into position. You can change AI difficulty between games using the Difficulty button. Wins are tracked on the leaderboard.

Four Across is a version of Connect Four, the game trademarked and published by Milton Bradley in 1974. Howard Wexler and Ned Strongin are credited with designing the commercial version. The idea of lining up four pieces in a row on a vertical grid may have been played informally before. The physical game uses a freestanding plastic grid where discs drop from the top. The column-stacking rule, where pieces fall to the bottom, is what makes it structurally different from other four-in-a-row games on flat boards.

Connect Four was mathematically solved in 1988 by James Dow Allen, and independently by Victor Allis in his master's thesis the same year. The result: the first player wins with perfect play, but only if they open in the center column. Every other opening lets the second player draw or win with perfect responses. This result is why strong programs and this game's AI both prioritize center-column placement. The 7x6 grid is the standard Connect Four size, chosen by Milton Bradley's design team to make the game deep enough for interesting play without being too slow.