connect: Implement the exercise "connect"

exercises/connect/README.md

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+# Connect
+
+Compute the result for a game of Hex / Polygon.
+
+The abstract boardgame known as
+[Hex](https://en.wikipedia.org/wiki/Hex_%28board_game%29) / Polygon /
+CON-TAC-TIX is quite simple in rules, though complex in practice. Two players
+place stones on a rhombus with hexagonal fields. The player to connect his/her
+stones to the opposite side first wins. The four sides of the rhombus are
+divided between the two players (i.e. one player gets assigned a side and the
+side directly opposite it and the other player gets assigned the two other
+sides).
+
+Your goal is to build a program that given a simple representation of a board
+computes the winner (or lack thereof). Note that all games need not be "fair".
+(For example, players may have mismatched piece counts.)
+
+The boards look like this (with spaces added for readability, which won't be in
+the representation passed to your code):
+
+```
+. O . X .
+ . X X O .
+  O O O X .
+   . X O X O
+    X O O O X
+```
+
+"Player `O`" plays from top to bottom, "Player `X`" plays from left to right. In
+the above example `O` has made a connection from left to right but nobody has
+won since `O` didn't connect top and bottom.
+
+### Submitting Exercises
+
+Note that, when trying to submit an exercise, make sure the solution is in the `exercism/python/<exerciseName>` directory.
+
+For example, if you're submitting `bob.py` for the Bob exercise, the submit command would be something like `exercism submit <path_to_exercism_dir>/python/bob/bob.py`.
+
+
+For more detailed information about running tests, code style and linting,
+please see the [help page](http://exercism.io/languages/python).
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

exercises/connect/connect.py

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+
+class ConnectGame:
+    def __init__(self, board):
+        pass

exercises/connect/connect_test.py

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+import unittest
+import connect
+
+testcases = [
+{
+    "description": "an empty board has no winner",
+    "board":
+	""" . . . . .
+	     . . . . .
+	      . . . . .
+	       . . . . .
+		. . . . .""",
+    "winner": ""
+},
+{
+    "description": "O can win on a 1x1 board",
+    "board": "O",
+    "winner": "O"
+},
+{
+    "description": "X can win on a 1x1 board",
+    "board": "X",
+    "winner": "X"
+},
+{
+    "description": "only edges does not make a winner",
+    "board":
+	""" O O O X
+	     X . . X
+	      X . . X
+	       X O O O""",
+    "winner": ""
+},
+{
+    "description": "illegal diagonal does not make a winner",
+    "board":
+	""" X O . .
+	     O X X X
+	      O X O .
+	       . O X .
+		X X O O""",
+    "winner": ""
+},
+{
+    "description": "nobody wins crossing adjacent angles",
+    "board":
+	""" X . . .
+	     . X O .
+	      O . X O
+	       . O . X
+		. . O .""",
+    "winner": ""
+},
+{
+    "description": "X wins crossing from left to right",
+    "board":
+	""" . O . .
+	     O X X X
+	      O X O .
+	       X X O X
+		. O X .""",
+    "winner": "X"
+},
+{
+    "description": "X wins using a convoluted path",
+    "board":
+	""" . X X . .
+	     X . X . X
+	      . X . X .
+	       . X X . .
+                O O O O O""",
+    "winner": "X"
+},
+{
+    "description": "O wins crossing from top to bottom",
+    "board":
+	""" . O . .
+	     O X X X
+	      O O O .
+	       X X O X
+		. O X .""",
+    "winner": "O"
+},
+{
+    "description": "X wins using a spiral path",
+    "board":
+	""" O X X X X X X X X
+	     O X O O O O O O O
+	      O X O X X X X X O
+	       O X O X O O O X O
+		O X O X X X O X O
+		 O X O O O X O X O
+		  O X X X X X O X O
+		   O O O O O O O X O
+		    X X X X X X X X O """,
+    "winner": "X"
+},
+]
+
+class SieveTest(unittest.TestCase):
+    def test_game(self):
+        for t in testcases:
+            winner = connect.play(t["board"])
+            expected = t["winner"] if t["winner"] else "None"
+            got = winner if winner else "None"
+            self.assertEqual(winner, t["winner"],
+                    "Test failed: %s, expected winner: %s, got: %s" % (t["description"], expected, got))
+
+if __name__ == '__main__':
+    unittest.main()

exercises/connect/example.py

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+
+class ConnectGame:
+
+    directions = [(0,1), (0,-1), (1,0), (-1,0), (1,-1), (-1,1)]
+    white = "O"
+    black = "X"
+    none = ""
+
+    def __init__(self, lines):
+        self.board = self.make_board(lines)
+        assert(len(self.board) > 0)
+
+        self.width = len(self.board[0])
+        self.height = len(self.board)
+        assert(self.width > 0 and self.height > 0)
+
+        for l in self.board:
+            assert(len(l) == self.width)
+
+    def valid(self, x, y):
+        return x >= 0 and x < self.width and y >= 0 and y < self.height
+
+    def make_board(self, lines):
+        return ["".join(l.split()) for l in lines.splitlines()]
+
+    def player_reach_dest(self, player, x, y):
+        if player == self.black:
+            return x == self.width - 1
+        if player == self.white:
+            return y == self.height - 1
+
+    def walk_board(self, player, x, y, visited=[]):
+        if (x, y) in visited:
+            return False
+
+        if (not self.valid(x, y)) or self.board[y][x] != player:
+            return False
+
+        if self.player_reach_dest(player, x, y):
+            return True
+
+        for d in self.directions:
+            if self.walk_board(player, x + d[0], y + d[1], visited + [(x,y)]):
+                return True
+
+    def check_player_is_winner(self, player):
+        if player == self.black:
+            return any([self.walk_board(player, 0, y) for y in range(self.height)])
+        if player == self.white:
+            return any([self.walk_board(player, x, 0) for x in range(self.width)])
+
+    def get_winner(self):
+        if self.check_player_is_winner(self.black):
+            return self.black
+        if self.check_player_is_winner(self.white):
+            return self.white
+        return self.none
+
+def play(board):
+    game = ConnectGame(board)
+    return game.get_winner()