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# queens.py # # ICS 3 3 Winter 2 0 2 4 # Project 0 : History of Modern # # A module containing tools

# queens.py
#
# ICS 33 Winter 2024
# Project 0: History of Modern
#
# A module containing tools that could assist in solving variants of the
# well-known "n-queens" problem. Note that we're only implementing one part
# of the problem: immutably managing the "state" of the board (i.e., which
# queens are arranged in which cells). The rest of the problem -- determining
# a valid solution for it -- is not our focus here.
#
# Your goal is to complete the QueensState class described below, though
# you'll need to build it incrementally, as well as test it incrementally by
# writing unit tests in test_queens.py. Make sure you've read the project
# write-up before you proceed, as it will explain the requirements around
# following (and documenting) an incremental process of solving this problem.
#
# DO NOT MODIFY THE Position NAMEDTUPLE OR THE PROVIDED EXCEPTION CLASSES.
from collections import namedtuple
from typing import Self
Position = namedtuple('Position',['row', 'column'])
# Ordinarily, we would write docstrings within classes or their methods.
# Since a namedtuple builds those classes and methods for us, we instead
# add the documentation by hand afterward.
Position.__doc__= 'A position on a chessboard, specified by zero-based row and column numbers.'
Position.row.__doc__= 'A zero-based row number'
Position.column.__doc__= 'A zero-based column number'
class DuplicateQueenError(Exception):
"""An exception indicating an attempt to add a queen where one is already present."""
def __init__(self, position: Position):
"""Initializes the exception, given a position where the duplicate queen exists."""
self._position = position
def __str__(self)-> str:
return f'duplicate queen in row {self._position.row} column {self._position.column}'
class MissingQueenError(Exception):
"""An exception indicating an attempt to remove a queen where one is not present."""
def __init__(self, position: Position):
"""Initializes the exception, given a position where a queen is missing."""
self._position = position
def __str__(self)-> str:
return f'missing queen in row {self._position.row} column {self._position.column}'
class QueensState:
"""Immutably represents the state of a chessboard being used to assist in
solving the n-queens problem."""
def __init__(self, rows: int, columns: int):
"""Initializes the chessboard to have the given numbers of rows and columns,
with no queens occupying any of its cells."""
pass
def queen_count(self)-> int:
"""Returns the number of queens on the chessboard."""
pass
def queens(self)-> list[Position]:
"""Returns a list of the positions in which queens appear on the chessboard,
arranged in no particular order."""
pass
def has_queen(self, position: Position)-> bool:
"""Returns True if a queen occupies the given position on the chessboard, or
False otherwise."""
pass
def any_queens_unsafe(self)-> bool:
"""Returns True if any queens on the chessboard are unsafe (i.e., they can
be captured by at least one other queen on the chessboard), or False otherwise."""
pass
def with_queens_added(self, positions: list[Position])-> Self:
"""Builds a new QueensState with queens added in the given positions.
Raises a DuplicateQueenException when there is already a queen in at
least one of the given positions."""
pass
def with_queens_removed(self, positions: list[Position])-> Self:
"""Builds a new QueensState with queens removed from the given positions.
Raises a MissingQueenException when there is no queen in at least one of
the given positions."""
pass

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