python to solve the eight queens problem

Using python generators can easily solve the eight queens problem

Tuple indicates possible solutions, where each element represents a position where corresponding row Queen (column), i.e., state [0] = 3, then the first row Queen in column 4.

# _*_ coding:utf-8 _*_
import random

#检测冲突
def conflict(state, nextX):         #state为各皇后相应位置
    nextY = len(state)
    for i in range(nextY):
        if abs(state[i] - nextX) in (0, nextY - i):    #下一个皇后与当前皇后在同一列或位于同一对角线
            return True
    return False

#递归
def queens(num=8, state=()):        #num为皇后数
    for pos in range(num):
        if not conflict(state, pos):
            if len(state) == num - 1:
                yield (pos,)
            else:
                for result in queens(num, state + (pos,)):
                    yield (pos,) + result
 
#图形输出（随机一结果）
def prettyprint(solution):        
    def line(pos, length=len(solution)):                #辅助函数
        return '. ' * (pos) + 'X ' + '. ' * (length-pos-1)
    for pos in solution:
        print(line(pos))
        
print(list(queens(4)))            #list()输出全部排序结果
print()
prettyprint(random.choice(list(queens(8))))  

The results show: