A console version of Connect Four written in Ruby.
Run ruby ./connect_four.rb.
Enter a number between 0 and 6 to choose which column to play in. To let the computer make the next move, enter c. The computer searches the game tree with the Minimax algorithm to a default depth of 4 plies. To change this, enter cx where x is a digit from 1 to 9 that indicates how many plies deep the AI should search. For example, c6 will make the computer make the next move with a search depth of 6.
Run rspec ./connect_four_move_node_spec.rb and rspec ./connect_four_move_tree_spec.rb.
See below for an example of what a game looks like in the console with two computer players. The column scores in the printout show the Minimax scores for each potential move. 1000 == guaranteed win. -1000 == guaranteed loss. 0 == tie or unknown outcome.
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
---------------
0 1 2 3 4 5 6
move? (0 through 6 or nothing for computer)
ai move: 5
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . 1 .
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 2 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: 0
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 2
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . 2 . . 1 .
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 1 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: 0
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 4
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . 2 . 1 1 .
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 2 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: 0
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 4
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . 2 . .
. . 2 . 1 1 .
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 1 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: 0
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 0
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . 2 . .
1 . 2 . 1 1 .
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 2 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: 0
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 5
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . 2 2 .
1 . 2 . 1 1 .
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 1 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: 0
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 2
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . 1 . 2 2 .
1 . 2 . 1 1 .
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 2 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: 0
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 0
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
2 . 1 . 2 2 .
1 . 2 . 1 1 .
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 1 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: 0
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 2
. . . . . . .
. . . . . . .
. . . . . . .
. . 1 . . . .
2 . 1 . 2 2 .
1 . 2 . 1 1 .
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 2 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: 0
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 6
. . . . . . .
. . . . . . .
. . . . . . .
. . 1 . . . .
2 . 1 . 2 2 .
1 . 2 . 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 1 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: 0
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 0
. . . . . . .
. . . . . . .
. . . . . . .
1 . 1 . . . .
2 . 1 . 2 2 .
1 . 2 . 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 2 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: 0
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 0
. . . . . . .
. . . . . . .
2 . . . . . .
1 . 1 . . . .
2 . 1 . 2 2 .
1 . 2 . 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 1 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: 0
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 5
. . . . . . .
. . . . . . .
2 . . . . . .
1 . 1 . . 1 .
2 . 1 . 2 2 .
1 . 2 . 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 2 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: 0
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 5
. . . . . . .
. . . . . . .
2 . . . . 2 .
1 . 1 . . 1 .
2 . 1 . 2 2 .
1 . 2 . 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 1 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: -1000
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 2
. . . . . . .
. . . . . . .
2 . 1 . . 2 .
1 . 1 . . 1 .
2 . 1 . 2 2 .
1 . 2 . 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 2 with depth 4:
Column 0 score: -1000
Column 1 score: -1000
Column 2 score: 0
Column 3 score: -1000
Column 4 score: -1000
Column 5 score: -1000
Column 6 score: -1000
move? (0 through 6 or nothing for computer)
ai move: 2
. . . . . . .
. . 2 . . . .
2 . 1 . . 2 .
1 . 1 . . 1 .
2 . 1 . 2 2 .
1 . 2 . 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 1 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: -1000
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 0
. . . . . . .
1 . 2 . . . .
2 . 1 . . 2 .
1 . 1 . . 1 .
2 . 1 . 2 2 .
1 . 2 . 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 2 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: 0
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 1
. . . . . . .
1 . 2 . . . .
2 . 1 . . 2 .
1 . 1 . . 1 .
2 . 1 . 2 2 .
1 2 2 . 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 1 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: -1000
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 1
. . . . . . .
1 . 2 . . . .
2 . 1 . . 2 .
1 . 1 . . 1 .
2 1 1 . 2 2 .
1 2 2 . 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 2 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: 0
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 6
. . . . . . .
1 . 2 . . . .
2 . 1 . . 2 .
1 . 1 . . 1 .
2 1 1 . 2 2 2
1 2 2 . 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 1 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: -1000
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 6
. . . . . . .
1 . 2 . . . .
2 . 1 . . 2 .
1 . 1 . . 1 1
2 1 1 . 2 2 2
1 2 2 . 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 2 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: 0
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 4
. . . . . . .
1 . 2 . . . .
2 . 1 . . 2 .
1 . 1 . 2 1 1
2 1 1 . 2 2 2
1 2 2 . 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 1 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: -1000
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 5
. . . . . . .
1 . 2 . . 1 .
2 . 1 . . 2 .
1 . 1 . 2 1 1
2 1 1 . 2 2 2
1 2 2 . 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 2 with depth 4:
Column 0 score: 0
Column 1 score: 0
Column 2 score: 0
Column 3 score: 0
Column 4 score: 0
Column 5 score: 0
Column 6 score: 0
move? (0 through 6 or nothing for computer)
ai move: 3
. . . . . . .
1 . 2 . . 1 .
2 . 1 . . 2 .
1 . 1 . 2 1 1
2 1 1 . 2 2 2
1 2 2 2 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 1 with depth 4:
Column 0 score: -1000
Column 1 score: -1000
Column 2 score: -1000
Column 3 score: 0
Column 4 score: -1000
Column 5 score: -1000
Column 6 score: -1000
move? (0 through 6 or nothing for computer)
ai move: 3
. . . . . . .
1 . 2 . . 1 .
2 . 1 . . 2 .
1 . 1 . 2 1 1
2 1 1 1 2 2 2
1 2 2 2 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 2 with depth 4:
Column 0 score: -1000
Column 1 score: -1000
Column 2 score: -1000
Column 3 score: -1000
Column 4 score: 0
Column 5 score: -1000
Column 6 score: -1000
move? (0 through 6 or nothing for computer)
ai move: 4
. . . . . . .
1 . 2 . . 1 .
2 . 1 . 2 2 .
1 . 1 . 2 1 1
2 1 1 1 2 2 2
1 2 2 2 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 1 with depth 4:
Column 0 score: -1000
Column 1 score: -1000
Column 2 score: -1000
Column 3 score: -1000
Column 4 score: 1000
Column 5 score: -1000
Column 6 score: -1000
move? (0 through 6 or nothing for computer)
ai move: 4
. . . . . . .
1 . 2 . 1 1 .
2 . 1 . 2 2 .
1 . 1 . 2 1 1
2 1 1 1 2 2 2
1 2 2 2 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 2 with depth 4:
Column 0 score: -1000
Column 1 score: -1000
Column 2 score: -1000
Column 3 score: -1000
Column 4 score: -1000
Column 5 score: -1000
Column 6 score: -1000
move? (0 through 6 or nothing for computer)
ai move: 5
. . . . . 2 .
1 . 2 . 1 1 .
2 . 1 . 2 2 .
1 . 1 . 2 1 1
2 1 1 1 2 2 2
1 2 2 2 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 1 with depth 4:
Column 0 score: 1000
Column 1 score: 1000
Column 2 score: 1000
Column 3 score: -1000
Column 4 score: 1000
Column 6 score: 1000
move? (0 through 6 or nothing for computer)
ai move: 6
. . . . . 2 .
1 . 2 . 1 1 .
2 . 1 . 2 2 1
1 . 1 . 2 1 1
2 1 1 1 2 2 2
1 2 2 2 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 2 with depth 4:
Column 0 score: -1000
Column 1 score: -1000
Column 2 score: -1000
Column 3 score: -1000
Column 4 score: -1000
Column 6 score: -1000
move? (0 through 6 or nothing for computer)
ai move: 4
. . . . 2 2 .
1 . 2 . 1 1 .
2 . 1 . 2 2 1
1 . 1 . 2 1 1
2 1 1 1 2 2 2
1 2 2 2 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 1 with depth 4:
Column 0 score: 1000
Column 1 score: 1000
Column 2 score: 1000
Column 3 score: -1000
Column 6 score: 1000
move? (0 through 6 or nothing for computer)
ai move: 1
. . . . 2 2 .
1 . 2 . 1 1 .
2 . 1 . 2 2 1
1 1 1 . 2 1 1
2 1 1 1 2 2 2
1 2 2 2 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 2 with depth 4:
Column 0 score: -1000
Column 1 score: -1000
Column 2 score: -1000
Column 3 score: -1000
Column 6 score: -1000
move? (0 through 6 or nothing for computer)
ai move: 0
2 . . . 2 2 .
1 . 2 . 1 1 .
2 . 1 . 2 2 1
1 1 1 . 2 1 1
2 1 1 1 2 2 2
1 2 2 2 1 1 2
---------------
0 1 2 3 4 5 6
Minimax algorithm results for player 1 with depth 4:
Column 1 score: 1000
Column 2 score: 1000
Column 3 score: 1000
Column 6 score: 1000
move? (0 through 6 or nothing for computer)
ai move: 1
2 . . . 2 2 .
1 . 2 . 1 1 .
2 1 1 . 2 2 1
1 1 1 . 2 1 1
2 1 1 1 2 2 2
1 2 2 2 1 1 2
---------------
0 1 2 3 4 5 6
Winner: 1