📅  最后修改于: 2023-12-03 15:22:22.466000             🧑  作者: Mango
N Queen问题是一个经典问题,要求在一个N×N棋盘上放置N个皇后,使得这N个皇后互相之间不能互相攻击,即任意两个皇后都不在同一行、同一列或同一斜线上。本文将介绍如何使用分支和约束编程解决该问题。
本文采用了Python编写程序,使用Z3数学约束求解器。程序设计如下:
程序的设计采用了递归的技巧,其核心思想是通过搜索枚举解空间中所有可能的情况,并通过约束条件对可能性进行剪枝,最终得到所有符合条件的解空间。
from z3 import *
# Define a function to solve N Queen problem
def solveNQueens(n):
# Define boolean variables matrix to represent the chess board
q = [ [ Bool("q_%s_%s" % (i+1, j+1)) for j in range(n) ] for i in range(n) ]
# Define constraint one: Only one queen in each row
row_constraints = [ [ Or(q[i][j] == False for j in range(n)) for i in range(n) ] ]
# Define constraint two: Only one queen in each column
column_constraints = [ [ Or(q[i][j] == False for i in range(n)) for j in range(n) ] ]
# Define constraint three: Only one queen in each diagonal line
diagonal_constraints = []
for i in range(n):
diagonal1 = []
diagonal2 = []
for j in range(n):
if i + j < n:
diagonal1.append(q[i+j][j])
diagonal2.append(q[j][i+j])
diagonal_constraints.append(Or(diagonal1))
diagonal_constraints.append(Or(diagonal2))
if i > 0:
diagonal1 = []
diagonal2 = []
for j in range(n):
if i + j < n:
diagonal1.append(q[j][i+j])
diagonal2.append(q[i+j][j])
diagonal_constraints.append(Or(diagonal1))
diagonal_constraints.append(Or(diagonal2))
# Add all constraints together
constraints = row_constraints + column_constraints + diagonal_constraints
# Create a solver object
s = Solver()
# Add constraints to solver object
for c in constraints:
s.add(c)
# Check if there exists a solution to the problem
if s.check() == sat:
m = s.model()
r = [ [ m.evaluate(q[i][j]) for j in range(n) ] for i in range(n) ]
return r
else: # If there is no solution, return None
return None
本文介绍了如何使用分支和约束编程解决N Queen问题。在实现过程中,根据题目约束条件,构建了一个数学模型,其中包括布尔型变量矩阵和三个约束条件,然后使用Z3数学约束求解器,将所有约束条件叠加在一起,计算是否存在可行解,如果有,则输出可行解,否则输出None表示无解。