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Replace Point class with dict in Backgammon code #798

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Merged
merged 1 commit into from
Mar 3, 2018
Merged

Replace Point class with dict in Backgammon code #798

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55 changes: 20 additions & 35 deletions games.py
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Original file line number Diff line number Diff line change
Expand Up @@ -75,7 +75,6 @@ def chance_node(state, action):
for val in dice_rolls:
game.dice_roll = val
sum_chances += min_value(res_state) * (1/36 if val[0] == val[1] else 1/18)

return sum_chances / num_chances

# Body of expectiminimax:
Expand Down Expand Up @@ -396,7 +395,7 @@ class Backgammon(Game):

def __init__(self):
self.dice_roll = (-random.randint(1, 6), -random.randint(1, 6))
board = Board()
board = BackgammonBoard()
self.initial = GameState(to_move='W',
utility=0, board=board, moves=self.get_all_moves(board, 'W'))

Expand Down Expand Up @@ -437,35 +436,35 @@ def get_all_moves(self, board, player):
at a given state."""
all_points = board.points
taken_points = [index for index, point in enumerate(all_points)
if point.checkers[player] > 0]
if point[player] > 0]
moves = list(itertools.permutations(taken_points, 2))
moves = moves + [(index, index) for index, point in enumerate(all_points)
if point.checkers[player] >= 2]
if point[player] >= 2]
return moves

def display(self, state):
"""Display state of the game."""
board = state.board
player = state.to_move
for index, point in enumerate(board.points):
if point.checkers['W'] != 0 or point.checkers['B'] != 0:
print("Point : ", index, " W : ", point.checkers['W'], " B : ", point.checkers['B'])
if point['W'] != 0 or point['B'] != 0:
print("Point : ", index, " W : ", point['W'], " B : ", point['B'])
print("player : ", player)


def compute_utility(self, board, move, player):
"""If 'W' wins with this move, return 1; if 'B' wins return -1; else return 0."""
count = 0
for idx in range(0, 24):
count = count + board.points[idx].checkers[player]
count = count + board.points[idx][player]
if player == 'W' and count == 0:
return 1
if player == 'B' and count == 0:
return -1
return 0


class Board:
class BackgammonBoard:
"""The board consists of 24 points. Each player('W' and 'B') initially
has 15 checkers on board. Player 'W' moves from point 23 to point 0
and player 'B' moves from point 0 to 23. Points 0-7 are
Expand All @@ -474,19 +473,20 @@ class Board:
def __init__(self):
"""Initial state of the game"""
# TODO : Add bar to Board class where a blot is placed when it is hit.
self.points = [Point() for index in range(24)]
self.points[0].checkers['B'] = self.points[23].checkers['W'] = 2
self.points[5].checkers['W'] = self.points[18].checkers['B'] = 5
self.points[7].checkers['W'] = self.points[16].checkers['B'] = 3
self.points[11].checkers['B'] = self.points[12].checkers['W'] = 5
point = {'W':0, 'B':0}
self.points = [point.copy() for index in range(24)]
self.points[0]['B'] = self.points[23]['W'] = 2
self.points[5]['W'] = self.points[18]['B'] = 5
self.points[7]['W'] = self.points[16]['B'] = 3
self.points[11]['B'] = self.points[12]['W'] = 5
self.allow_bear_off = {'W': False, 'B': False}

def checkers_at_home(self, player):
"""Returns the no. of checkers at home for a player."""
sum_range = range(0, 7) if player == 'W' else range(17, 24)
count = 0
for idx in sum_range:
count = count + self.points[idx].checkers[player]
count = count + self.points[idx][player]
return count

def is_legal_move(self, start, steps, player):
Expand All @@ -498,7 +498,7 @@ def is_legal_move(self, start, steps, player):
dest_range = range(0, 24)
move1_legal = move2_legal = False
if dest1 in dest_range:
if self.points[dest1].is_open_for(player):
if self.is_point_open(player, self.points[dest1]):
self.move_checker(start[0], steps[0], player)
move1_legal = True
else:
Expand All @@ -508,7 +508,7 @@ def is_legal_move(self, start, steps, player):
if not move1_legal:
return False
if dest2 in dest_range:
if self.points[dest2].is_open_for(player):
if self.is_point_open(player, self.points[dest2]):
move2_legal = True
else:
if self.allow_bear_off[player]:
Expand All @@ -519,30 +519,15 @@ def move_checker(self, start, steps, player):
"""Moves a checker from starting point by a given number of steps"""
dest = start + steps
dest_range = range(0, 24)
self.points[start].remove_checker(player)
self.points[start][player] -= 1
if dest in dest_range:
self.points[dest].add_checker(player)
self.points[dest][player] += 1
if self.checkers_at_home(player) == 15:
self.allow_bear_off[player] = True

class Point:
"""A point is one of the 24 triangles on the board where
the players' checkers are placed."""

def __init__(self):
self.checkers = {'W':0, 'B':0}

def is_open_for(self, player):
def is_point_open(self, player, point):
"""A point is open for a player if the no. of opponent's
checkers already present on it is 0 or 1. A player can
move a checker to a point only if it is open."""
opponent = 'B' if player == 'W' else 'W'
return self.checkers[opponent] <= 1

def add_checker(self, player):
"""Place a player's checker on a point."""
self.checkers[player] += 1

def remove_checker(self, player):
"""Remove a player's checker from a point."""
self.checkers[player] -= 1
return point[opponent] <= 1