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Project description

In this project, we will implement agent that plays the game of Pente, the two-player version of
the abstract strategy board game. It is in the m,n,k-game family from which tic-tac-toe (3,3,3)
and Connect Four also come from, where the players are trying to connect k pieces on the
board before the other player does.

Pente stands out from these games because it includes a
piece capture mechanic, where the player can sandwich a pair of their opponent’s pieces and
capture them. It is played on a 19×19 board, where pieces are placed on the intersection of the
lines (like the game Go). White always opens the game (like in Chess).

The players take turns
putting pieces on the board until:
1) A player connects 5 of their pieces in a horizontal, vertical or a diagonal line, OR
2) A player makes 5 total captures (equals to 10 pieces of their opponent’s since pieces can
only be captured in pairs).

The custodial capture mechanic, where a player flanks the opponent’s pieces with their own to
capture them, only applies to pairs of the opponent’s pieces. Therefore, if the current board
formation is XOO_ and player X plays their piece as XOOX, the O pieces are captured and the
board becomes X_ _X.

Note again that this only works for pairs of pieces, therefore X cannot
capture their opponent’s pieces from a board like XOOO_ or XO_.
Captures only happen when a capturing piece is placed. Therefore, if the board is XO_X and O
places a piece in the free intersection, the board formation becomes XOOX and no capture
happens by X.

More details on the game can be found at https://en.wikipedia.org/wiki/Pente and we will also
go over the gameplay for you below (be careful, Wikipedia images show a 13×13 board). If you
would like to try the game of Pente to understand the general gameplay, you can utilize the “Play
the AI” option without having to log in at https://pente.org/join.jsp.

Note that these resources
are just for you to familiarize yourself with the game, you should strictly follow the rules we
outline below while coding your game-playing agent (there are several variants of the game).
The original Pente game is known to favor the first player. This is called the First Player
Advantage (FPA) and there has been many suggestions to level the playing field for the second
player. A discussion about this can be found in:
https://en.wikipedia.org/wiki/Pente#First_Player_Advantage

We will be employing certain rules that have been used in the past in Pente tournaments to make
this game fairer for the second player. More details of these can be found below. These will also
help us determine how winners are determined in student competitions.

Setup of the game:

The setup of the game is as follows:
– Each player plays as white or black.
– The board consists of an 19×19 grid of squares.
– Before the game starts, the board is empty.
– White always opens the game.
– First piece (White) must be placed in the middle of the board.
– The second move of White (first player) cannot be less than 3 intersections away from
their first piece (center). This is one of the rules that alleviates the first player advantage
(FPA).
– Pieces can be placed in any empty intersection (apart from the first player restrictions
explained above).

– Placed pieces cannot be removed from the board unless they are captured.
Here’s the visualization of an empty board and an example start, just after White has placed their
second piece following the anti-FPA restriction:
As can be seen in the right image above, White has placed their 2nd piece 3 intersections away
which is the maximum possible amount for their second move. In following turns, pieces can be
placed in any empty intersection, but your agent should be able to figure out which is best.

Play sequence:

We first describe the typical play for humans. We will then describe some minor modifications
for how we will play this game with artificial agents.
– Create the initial board setup according to the above description.
– Players randomly determine who will play White/Black. White will play first.
– During their turn, each player places a single piece of one’s own color on the board:
o Once placed, the pieces cannot be removed from their intersection unless they
are captured by the opponent.

o A simple move:
§ Can be played on any empty intersection (including border intersections).
§ If playing White, player must place their 1st piece in the center of the board
and their 2nd piece no less than 3 intersections away from the 1st piece.
o A capture move:
§ Is played next to a pair of the opponent’s pieces such that they are flanked
(sandwiched) by one of the player’s pieces. The opponent’s pieces are
captured by the player when this happens.

A sample capture can be seen below:

§ The capture can be made for pieces that are horizontally, vertically, or
diagonally oriented.
§ When capture happens, the pair of pieces belonging to the opponent are
removed from the board and added to the player’s capture pile.
§ One capture move can be used to capture one or more pairs of pieces from
the opponent. Sample of this can be seen below:

§ Note that captures only happen when both of the opponent’s pieces are
on the board when a capturing move is made. Therefore, if the board state
is XO_X and O moves to make it XOOX, the pair of O pieces are not
captured by X. An example for this is below.
– If the current play results in a board where the active player has 5+ connected pieces on
the board OR has 5 pairs (or 10 pieces) total captured from their opponent, the game
ends. Otherwise, play proceeds to the other player.

– If above conditions are not met, and there is no more room left on the board to play a
piece, the game ends in a draw.

Playing with agents

In this homework, your agent will play against another agent, either implemented by the TAs, or
by another student in the class.
For grading, your agent will play against two different agents implemented by the TAs. 10 full
games will be against a random agent (this should be easy for your agent to beat), and another
10 full games will be against a simple minimax agent with no alpha-beta pruning.

There will be a
limited total amount of play time available to your agent for the whole game (e.g., 100 seconds),
so you should think about how to best use it throughout the game. This total amount of time will
vary from game to game. Your agent must play correctly (no illegal moves, etc.) and beat the
reference agents to receive 5 points per game.

Your agent will be given the first move on 12 of
the 20 games. In case of a draw, the agent with more remaining play time wins. Note that, while
playing games, you should think about how to divide your remaining play time across possibly
many moves throughout the game.

In addition to grading, we will run a competition where your agent plays against agents created
by the other students in the class. This will not affect your grade, but it would look very good on
your Resume if you finish in the top 10, or are the grand winner!

Agent vs agent games:

Playing against another agent will be organized as follows (both when your agent plays against
the reference minimax agent, or against another student’s agent):
A master game playing engine will be implemented by the grading team. This engine will:
– Create the initial board setup according to the above description.
– Assign a player color (Black or White) to your agent. The player who gets assigned White
will have the first move.

– Then, in sequence, until the game is over:
o The master game playing engine will create an input.txt file which contains the
current board configuration, which color your agent should play, and how much
total play time your agent has left. This file will also contain number of pieces
captured by each agent until that point in the game. More details on the exact
format of input.txt are given below.

o We will then run your agent. Your agent should read input.txt in the current
directory, decide on a move, and create an output.txt file that describes the move
(details below). Your time will be measured (total CPU time). If your agent does
not return before your time is over, it will be killed and it loses the game.
o Your remaining playing time will be updated by subtracting the time taken by your
agent on this move. If time left reaches zero or negative, your agent loses the
game.

o The validity of your move will be checked. If the format of output.txt is incorrect
or your move is invalid according to the rules of the game, your agent loses the
game. (Reminder: Any empty spot on the board is a valid move, except for the
rules for the first two moves of the white player.)
o Your move will be executed by the master game playing engine. This will update
the game board to a new configuration.

o The master game playing engine will check for a game-over condition. If one
occurs, the winning agent or a draw will be declared accordingly.
o The master game playing engine will then present the updated board to the
opposing agent and let that agent make one move (with the same rules as just
described for your agent; the only difference is that the opponent plays the other
color and has its own time counter).
o Game continues until an end condition is reached.

Input and output file formats:

Input: The file input.txt in the current directory of your program will be formatted as follows:
First line: A string BLACK or WHITE indicating which color you play. White will always start
the game.
Second line: A strictly positive floating point number indicating the amount of play time
remaining for your agent (in seconds).

Third line: Two non-negative 32-bit integers separated by a comma indicating the number of
pieces captured by White and Black players consecutively. Caution, it will always
be ordered as first captured by White, then by Black, irrespective of what color is
given in the first line.

Next 19 lines: Description of the game board, with 19 lines of 19 symbols each:
§ w for a cell occupied by a white piece
§ b for a cell occupied by a black piece
§ . (a dot) for an empty intersection
For example:
BLACK
100.0
0,0

……………….
……………….
……………….
……………….
……………….
……………….
……………….

………w………
……….b……..
………w.bw……
……………….
……………….
……………….
……………….
……………….
……………….
……………….
……………….
……………….

In this input.txt example, your agent should play a move as the Black agent and has 100.0
seconds. The board configuration is 5 turns into the game. There’s a capture condition for
White, so your agent could likely choose to block that by putting their piece in the red
highlighted position on the board.

Output:

The format we will use for describing the square positions is borrowed from the
notations from Pente.org, where every column is described by a letter and every row is described
by a number. The position for a given square is given as the concatenation of these. Here’s a
useful visualization on how we identify each intersection for the 19×19 Pente board:

Using the above image as reference, in the input.txt sample given above, White has pieces on
10K, 10N and 12K, while Black has pieces on 11L and 10M. Using this type of notation for the cells
on our gameboard, the file output.txt which your program creates in the current directory should
be formatted as follows:

1 line: PIECE_POS which describes your move with an integer (1-19) and an uppercase letter
(A-T) concatenated.
For example, for the red highlighted move in the input sample, output.txt may contain:
9N
The resulting board would look like this, given the above input.txt (the master game playing
engine will compute this and it is not part of output.txt):

……………….
……………….
……………….
……………….
……………….
……………….
……………….
………w………
……….b……..
………w.bw……

…………b……
……………….
……………….
……………….
……………….
……………….
……………….
……………….
……………….

Notes and hints:

– Please name your program “homework.xxx” where ‘xxx’ is the extension for the
programming language you choose (“py” for python, “cpp” for C++11, and “java” for
Java).
– The board you will be given as input will always be valid and will have w and b letters, as
well as . (standing for empty cells).
– Likely (but not guaranteed), total play time will be 5 minutes (300.0 seconds) when
playing against another agent.

– Play time used on each move is the total combined CPU time as measured by the Unix
time command. This command measures pure computation time used by your agent,
and discards time taken by the operating system, disk I/O, program loading, etc. Beware
that it cumulates time spent in any threads spawned by your agent (so if you run 4 threads
and use 400% CPU for 10 seconds, this will count as using 40 seconds of allocated time).
– If your agent runs for more than its given play time (in input.txt), it will be killed and will
lose the game.

– You need to think and strategize how to best use your allocated time. In particular, you
need to decide on how deep to carry your search, on each move. In some cases, your
agent might be given only a very short amount of time (e.g., 5.2 seconds, or even 0.01
seconds), for example towards the end of a game.

Your agent should be prepared for that
and return a quick decision to avoid losing by running over time. The amount of play time
that will be given in input.txt will always be >0, but it could be very small if you are close
to running out of time.

– To help you with figuring out the speed of the computer that your agent runs on, you are
allowed to also provide a second program called calibrate.xxx (same extension
conventions as for homework.xxx). This is optional. If one is present, we will run your
calibrate program once (and only once) before we run your agent for grading or against
another agent.

You can use calibrate to, e.g., measure how long it takes to expand some
fixed number of search nodes, or to benchmark the CPU speed in any other way you like.
You can then save this into a single file called calibration.txt in the current directory.
When your agent runs during grading or during a game, it could then read calibration.txt
in addition to reading input.txt, and use the data from calibration.txt to strategize about
search depth or other factors.

Please aim for no more than 5 minutes to run your calibrate
program. A few seconds (e.g., expand 10,000 nodes) is usually enough to get a good
estimate of the CPU speed.

– You need to think hard about how to design your eval function (which gives a value to a
board when it is not game over yet).
– You are allowed to maintain persistent data across moves during a game, by writing such
data to a single file called playdata.txt in the current directory. Before a new game starts,
the master game playing engine will delete any playdata.txt file.

So, on your first move,
this file will not exist, and you should be prepared for that. Then, you can write some data
to that file at the end of a move and read that file back at the beginning of the next move.
– As mentioned, there is some first player advantage in this game for two agents with
perfect play (even with our rules for the first two White moves). Therefore, when playing
against a reference agent, we will give your agent the first move for 6 of the 10 games.

In
the competition, we will play two agents against each other for an even number of games
giving each the first player for half of the games, and advance both agents to the next
round of the competition if they both win or draw on half of the games. If an agent loses
more than half of the games, it will be eliminated and only the other agent will move to
the next round of the competition. We may end up with several equivalent winners of the
competition.

– The random agent created by the TAs will likely not be uniformly random over the whole
board, but may choose randomly between several candidate locations, for example all
locations adjacent to pieces already on the board.

The minimax TA agent will not use
alpha-beta and will likely be capped at a low lookahead depth; but it will do adaptive
depth choice on every move to avoid running out of time (e.g., use depth 3 when >50s
remains, depth 1 when < 3s, otherwise depth 2).