From 15941aa3d878b685b88dc6c80c677520e4a8b096 Mon Sep 17 00:00:00 2001
From: Shubham Sharma <klusbn@gmail.com>
Date: Mon, 21 Oct 2019 13:09:33 +0530
Subject: [PATCH] Create tictactoe_minimax.py

TicTacToe game which uses minimax algorithm.
---
 tictactoe_minimax.py | 142 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 142 insertions(+)
 create mode 100644 tictactoe_minimax.py

diff --git a/tictactoe_minimax.py b/tictactoe_minimax.py
new file mode 100644
index 0000000..9b91295
--- /dev/null
+++ b/tictactoe_minimax.py
@@ -0,0 +1,142 @@
+import random
+
+
+class TicTacToe:
+    def __init__(self, playerX, playerO):
+        self.board = [' '] * 9
+        self.playerX, self.playerO = playerX, playerO
+        self.playerX_turn = True
+
+    def display_board(self):
+        print ('     |     |     ')
+        print ('  %s  |  %s  |  %s  ' % (self.board[0],
+                                        self.board[1],
+                                        self.board[2]))
+        print ('_____|_____|_____')
+        print ('     |     |     ')
+        print ('  %s  |  %s  |  %s  ' % (self.board[3],
+                                        self.board[4],
+                                        self.board[5]))
+        print ('_____|_____|_____')
+        print ('     |     |     ')
+        print ('  %s  |  %s  |  %s  ' % (self.board[6],
+                                        self.board[7],
+                                        self.board[8]))
+        print ('     |     |     ')
+
+    def board_full(self):
+        return not any([space == ' ' for space in self.board])
+
+    def player_wins(self, char):
+        for a, b, c in [(0, 1, 2), (3, 4, 5), (6, 7, 8),
+                        (0, 3, 6), (1, 4, 7), (2, 5, 8),
+                        (0, 4, 8), (2, 4, 6)]:
+            if char == self.board[a] == self.board[b] == self.board[c]:
+                return True
+
+        return False
+
+    def play_game(self):
+        print ('\nNew game!')
+
+        while True:
+            if self.playerX_turn:
+                player, char = self.playerX, 'X'
+            else:
+                player, char = self.playerO, 'O'
+
+            if player.breed == 'human':
+                self.display_board()
+
+            move = player.move(self.board)
+            self.board[move - 1] = char
+
+            if self.player_wins(char):
+                self.display_board()
+                print (char + ' wins!')
+                break
+
+            if self.board_full():
+                self.display_board()
+                print ('Draw!')
+                break
+
+            self.playerX_turn = not self.playerX_turn
+
+
+class Player(object):
+    def __init__(self):
+        self.breed = 'human'
+
+    def move(self, board):
+        return int(input('Your move? '))
+
+    def available_moves(self, board):
+        return [i + 1 for i in range(0, 9) if board[i] == ' ']
+
+
+class MinimaxPlayer(Player):
+    def __init__(self):
+        self.breed = 'minimax'
+
+    def move(self, board):
+        if len(self.available_moves(board)) == 9:
+            return random.choice([1, 3, 7, 9])
+
+        best_value = 0
+        for move in self.available_moves(board):
+            board[move - 1] = 'X'
+            value = self.min_value(board)
+            board[move - 1] = ' '
+            if value > best_value:
+                return move
+
+        return random.choice(self.available_moves(board))
+
+    def terminal_test(self, board):
+        for a, b, c in [(0, 1, 2), (3, 4, 5), (6, 7, 8),
+                        (0, 3, 6), (1, 4, 7), (2, 5, 8),
+                        (0, 4, 8), (2, 4, 6)]:
+            if 'X' == board[a] == board[b] == board[c]:
+                return (True, 1)
+            elif 'O' == board[a] == board[b] == board[c]:
+                return (True, -1)
+
+        if not any([space == ' ' for space in board]):
+            return (True, 0)
+
+        return (False, 0)
+
+    def max_value(self, board):
+        in_terminal_state, utility_value = self.terminal_test(board)
+        if in_terminal_state:
+            return utility_value
+
+        value = -100000
+        for move in self.available_moves(board):
+            board[move - 1] = 'X'
+            value = max(value, self.min_value(board))
+            board[move - 1] = ' '
+
+        return value
+
+    def min_value(self, board):
+        in_terminal_state, utility_value = self.terminal_test(board)
+        if in_terminal_state:
+            return utility_value
+
+        value = 100000
+        for move in self.available_moves(board):
+            board[move - 1] = 'O'
+            value = min(value, self.max_value(board))
+            board[move - 1] = ' '
+
+        return value
+
+
+p1 = MinimaxPlayer()
+p2 = Player()
+
+while True:
+    t = TicTacToe(p1, p2)
+    t.play_game()