Given the position of two queens on a chess board, indicate whether or not they are positioned so that they can attack each other.
In the game of chess, a queen can attack pieces which are on the same row, column, or diagonal.
A chessboard can be represented by an 8 by 8 array.
So if you're told the white queen is at (2, 3) and the black queen at (5, 6), then you'd know you've got a set-up like so:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ W _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ B _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
You'd also be able to answer whether the queens can attack each other. In this case, that answer would be yes, they can, because both pieces share a diagonal.
Sometimes it is necessary to raise an exception. When you do this, you should include a meaningful error message to indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. Not every exercise will require you to raise an exception, but for those that do, the tests will only pass if you include a message.
To raise a message with an exception, just write it as an argument to the exception type. For example, instead of
raise Exception, you should write:
raise Exception("Meaningful message indicating the source of the error")
To run the tests, run the appropriate command below (why they are different):
Alternatively, you can tell Python to run the pytest module (allowing the same command to be used regardless of Python version):
python -m pytest queen_attack_test.py
-v: enable verbose output
-x: stop running tests on first failure
--ff: run failures from previous test before running other test cases
For other options, see
python -m pytest -h
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J Dalbey's Programming Practice problems http://users.csc.calpoly.edu/~jdalbey/103/Projects/ProgrammingPractice.html
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
import unittest from queen_attack import Queen # Tests adapted from `problem-specifications//canonical-data.json` @ v2.1.0 class QueenAttackTest(unittest.TestCase): # Test creation of Queens with valid and invalid positions def test_queen_valid_position(self): try: Queen(2, 2) except ValueError: self.fail("Unexpected Exception") def test_queen_negative_row(self): with self.assertRaisesWithMessage(ValueError): Queen(-2, 2) def test_queen_invalid_row(self): with self.assertRaisesWithMessage(ValueError): Queen(8, 4) def test_queen_negative_column(self): with self.assertRaisesWithMessage(ValueError): Queen(2, -2) def test_queen_invalid_column(self): with self.assertRaisesWithMessage(ValueError): Queen(4, 8) # Test the ability of one queen to attack another def test_attack_false(self): self.assertIs(Queen(2, 4).can_attack(Queen(6, 6)), False) def test_attack_same_row(self): self.assertIs(Queen(2, 4).can_attack(Queen(2, 6)), True) def test_attack_same_column(self): self.assertIs(Queen(4, 5).can_attack(Queen(2, 5)), True) def test_attack_diagonal1(self): self.assertIs(Queen(2, 2).can_attack(Queen(0, 4)), True) def test_attack_diagonal2(self): self.assertIs(Queen(2, 2).can_attack(Queen(3, 1)), True) def test_attack_diagonal3(self): self.assertIs(Queen(2, 2).can_attack(Queen(1, 1)), True) def test_attack_diagonal4(self): self.assertIs(Queen(2, 2).can_attack(Queen(5, 5)), True) # Track-specific tests def test_queens_same_position_can_attack(self): with self.assertRaisesWithMessage(ValueError): Queen(2, 2).can_attack(Queen(2, 2)) # Utility functions def setUp(self): try: self.assertRaisesRegex except AttributeError: self.assertRaisesRegex = self.assertRaisesRegexp def assertRaisesWithMessage(self, exception): return self.assertRaisesRegex(exception, r".+") if __name__ == '__main__': unittest.main()
class Board: EMPTY_BOARD = ["_" * 8 for _ in range(8)] def __init__(self, white_coords, black_coords): self.white_coords = white_coords self.black_coords = black_coords if not self.valid_coords(): raise ValueError self.board = self.generate_board() def generate_board(self): board = map(lambda row: list(row), self.EMPTY_BOARD) board = self.place_piece(board, "W", self.white_coords) board = self.place_piece(board, "B", self.black_coords) return map(lambda row: "".join(row), board) def can_attack(self): return self.same_row() or self.same_col() or self.same_diag() def same_row(self): return self.white_coords == self.black_coords def same_col(self): return self.white_coords == self.black_coords def same_diag(self): return (abs(self.white_coords - self.black_coords) == abs(self.white_coords - self.black_coords)) def valid_coords(self): return (self.different_coords() and self.valid_coord(self.white_coords) and self.valid_coord(self.black_coords)) def different_coords(self): return self.white_coords != self.black_coords @staticmethod def valid_coord(coord): return (0 <= coord <= 7 and 0 <= coord <= 7) @staticmethod def place_piece(board, piece, coords): board[coords][coords] = piece return board def board(white_coords, black_coords): return Board(white_coords, black_coords).board def can_attack(white_coords, black_coords): return Board(white_coords, black_coords).can_attack()
A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.
Here are some questions to help you reflect on this solution and learn the most from it.