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The Connect-4 game board consists of 7 vertical slots or columns, numbered from 0 to 6, each of which can accommodate up to 6 tokens. Two players take turns to place a token in a slot, we're calling them Red and Yellow. The winner is the first player who has 4 of their tokens in a line, horizontally, vertically or diagonally.
Although the game can be fully solved with enough effort, a fair-to-average player can be simulated by scoring possible game positions and looking only a couple of plies ahead (a ply is an action by one player, two plies make up a move). The scoring system assigns points to each sequence of a player's tokens that have a reasonable chance of becoming a winning line. The scoring system to use for this task is as follows:
The board is represented by 7 fixed-length strings, one for each vertical slot or column. This format best suits operations such as temporarily adding or removing a token, used in game play. Each character is a token (R or Y) or an empty position (a dot). Every legal board column thus begins with zero or more tokens, then empty symbols to make up 6 characters. You can use a different internal representation of course, but input/output uses this format.
Consider the following board:
RR.... ...... YRRYR. YYR... RYYR.. RYY... Y.....It scores 37 for player R (majority in col 2, pair in col 0, pair in row 2 and a diagonal line of three producing a triple at one end and a PWP at the other). For player Y the same board scores 44 (centre col majority, pair in col 5, triple on row 1, two diagonal triples in one direction and one in the other).
Write a program that can read boards and score them for a designated player, and for full marks, can also play a full game against a player using a limited strategy. Input consists of board layouts preceded by a line containing score and either R or Y. A line containing the word end terminates the input. Output is a copy of the board in the same format (so we know you've read it properly) and the nominated player and calculated score on the next line. If you were scoring R for the above layout the output would be
RR.... ...... YRRYR. YYR... RYYR.. RYY... Y..... Player R scores 37
To play the game (say after processing the normal input), use the following strategy exactly:
R..... Y..... YRRY.. YYRY.. RYR... R..... Y..... Move 9: scores 48-29, 34-40, 47-29, 45-29, 54-20, 37-37, 45-26 R selects column 4 Reply score 20 Y selects column 5 R..... Y..... YRRY.. YYRY.. RYRR.. RY.... Y.....
Test your program using the following data.
score Y ...... YRR... YY.... YRR... RRR... YYY... RRY... score R ...... YR.... RYR... YYRRY. YRYYY. RRY... RRY... score Y RYRYY. RYY... RRRYR. YRY... RYRY.. R..... RRR... score R RRYRYY YRY... YRRRYR RYRY.. YRYRY. ...... RRR... score Y YRYRY. RYRYR. YRYRY. YRYRYR RRYRR. Y..... RY.... score R RYRY.. YRYR.. YRR... RYYR.. RYY... YRYR.. RYRY.. end
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