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# queens.py
# From Classic Computer Science Problems in Python Chapter 3
# Copyright 2018 David Kopec
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from csp import Constraint, CSP
from typing import Dict, List, Optional
class QueensConstraint(Constraint[int, int]):
def __init__(self, columns: List[int]) -> None:
super().__init__(columns)
self.columns: List[int] = columns
def satisfied(self, assignment: Dict[int, int]) -> bool:
# q1c = queen 1 column, q1r = queen 1 row
for q1c, q1r in assignment.items():
# q2c = queen 2 column
for q2c in range(q1c + 1, len(self.columns) + 1):
if q2c in assignment:
q2r: int = assignment[q2c] # q2r = queen 2 row
if q1r == q2r: # same row?
return False
if abs(q1r - q2r) == abs(q1c - q2c): # same diagonal?
return False
return True # no conflict
if __name__ == "__main__":
columns: List[int] = [1, 2, 3, 4, 5, 6, 7, 8]
rows: Dict[int, List[int]] = {}
for column in columns:
rows[column] = [1, 2, 3, 4, 5, 6, 7, 8]
csp: CSP[int, int] = CSP(columns, rows)
csp.add_constraint(QueensConstraint(columns))
solution: Optional[Dict[int, int]] = csp.backtracking_search()
if solution is None:
print("No solution found!")
else:
print(solution)