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# Connect Four

Connect Four (also known as Plot Four) is a two-player board game in which the objective is to be the first to get four of one's own discs in a line.

The game is played on a 7x6 board which is placed in a vertical position. The players take turns in dropping discs in one of the columns. The column must not be full; the disc then occupies the lowest unoccupied square on that column. The game ends when one of the players obtains 4 of their own discs consecutively in a line (row, column or diagonal).

Connect Four has been solved independently by Victor Allis and James D. Allen. It is a win for the first player. The perfect play strategy starts with a move in the middle column; all other opening moves can be drawn by the second player.

## Strategy

A Connect Four game in progress
()

In the short term, one should aim to force a win by making two threats simultaneously; conversely, one should prevent the opponent from doing so. For instance, in the figure on the right, it is green's turn. Yellow will win on their next turn irrespective of green's move because of the threat of extending the diagonal of three consecutive yellow discs to four by dropping a disc either on the third or on the last column, not both of which can be blocked by green.

The long term strategy is more complex. Towards the end of the game, when there are few columns that aren't fully filled, sequences of many moves on the same column often result. Further, it is likely that the first player will fill the odd numbered rows and the second player the even numbered rows (assuming the bottom row is numbered 1). Therefore, on each column, the first player should try to get a threat on as low an odd numbered row as possible and the second player on as low an even numbered square as possible.