python回溯法八皇后问题

八皇后问题是一个经典的回溯法问题，目标是在一个8x8的棋盘上放置8个皇后，使得它们互相之间不能攻击到对方。这里是一个Python的八皇后问题的回溯法解法：

def solve_n_queens(n):
def could_place(row, col):
return not (cols[col] + hill_diagonals[row - col] + dale_diagonals[row + col])

def place_queen(row, col):
queens.add((row, col))
cols[col] = 1
hill_diagonals[row - col] = 1
dale_diagonals[row + col] = 1

def remove_queen(row, col):
queens.remove((row, col))
cols[col] = 0
hill_diagonals[row - col] = 0
dale_diagonals[row + col] = 0

def add_solution():
solution = []
for _, col in sorted(queens):
solution.append('.' * col + 'Q' + '.' * (n - col - 1))
output.append(solution)

def backtrack(row = 0):
for col in range(n):
if could_place(row, col):
place_queen(row, col)
if row + 1 == n:
add_solution()
else:
backtrack(row + 1)
remove_queen(row, col)

cols = [0] * n
hill_diagonals = [0] * (2 * n - 1)
dale_diagonals = [0] * (2 * n - 1)
queens = set()
output = []
backtrack()
return output

print(solve_n_queens(8))

这个代码使用了回溯法来解决八皇后问题，它会返回所有可能的解法。