Wikipedia

Connect Four

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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 was published by Milton Bradley in 1974; a non-proprietary version is known as "The Captain's Mistress".

Rules

The game is played on a board with 7 columns and 6 rows, which is placed in a vertical position. The players have 21 discs each, distinguished by color. The players take turns in dropping discs in one of the non-full columns. The disc then occupies the lowest unoccupied square on that column. A player wins if they succeed in placing four of their own discs consecutively in a line (row, column or diagonal), which ends the game. The game ends in a draw if the board is filled completely without any player winning.

Strategy and Tactics

Beginners will often overlook a simple threat to connect four discs; it is therefore important to always check all vertical, horizontal and diagonal lines.

File:Connect four game small.png

A Connect Four game in progress


In more advanced play, one aims at forcing 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, only one of which can be blocked by green.

As a general rule of thumb, discs played in the center columns are more valuable than border column discs, because they participate in more potential four-disc lines (and accordingly limit the opponent's opportunities).

Among good players, the short term goal is to connect three discs, thereby preventing the opponent from playing in a certain column. Towards the end, the game then often turns into a complex counting match: both players try to win by forcing the other to play a certain column. In these situations, it is useful to realize that, if it's your move, then after filling an even number of places, it's still your move. Every column has an even number of places.

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. It is also important to understand that a threat is useless if the opponent already has a threat in the same columnn and an odd number of rows below yours.

Perfect play

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.

Trivia

Connect Four is popular in the beer bars of Thailand, and the experienced prostitutes working there are often surprisingly strong players.

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