python解决拉斯维加斯算法求n皇后问题，并输出结果

这里提供一个Python解决n皇后问题的拉斯维加斯算法实现，代码如下：

import random

def n_queens(n):
    board = [-1] * n
    attempts = 0
    while True:
        col = random.randint(0, n-1)
        row = find_available_row(col, board)
        if row is not None:
            board[col] = row
            if col == n-1:
                return board
        else:
            board[col] = -1
        attempts += 1
        if attempts > 3 * n:
            board = [-1] * n
            attempts = 0

def find_available_row(col, board):
    n = len(board)
    rows = list(range(n))
    random.shuffle(rows)
    for row in rows:
        if is_safe(row, col, board):
            return row
    return None

def is_safe(row, col, board):
    for c, r in enumerate(board):
        if r == row or c-r == col-row or c+r == col+row:
            return False
    return True

n = 8
board = n_queens(n)
if board is not None:
    for row in board:
        line = ['.'] * n
        line[row] = 'Q'
        print(' '.join(line))
else:
    print('Failed to find a solution.')

该算法思想是随机选择一个列，然后在该列中随机选择一个行放置皇后，如果该位置不安全，则重新选择。如果找到了合法的皇后布局，则返回结果。如果多次尝试后仍然没有找到合法的皇后布局，则重新开始。该算法的时间复杂度是O(n!)，但是由于随机性使得其在实际运行中的效率和表现比较好。