八皇后问题

语言：python

 1 # state[0] = 1 to represent a queen
 2 # state = (1,3,0,2)
 3 # * Q * *
 4 # * * * Q 
 5 # Q * * *
 6 # * * Q *
 7 def conflict(state, nextX):
 8     nextY = len(state)
 9 
10     for i in range(nextY):
11         if abs(state[i] - nextX) in (0, nextY - i):
12             return True
13 
14     return False

使用yield

 1 def queens(num, state):
 2     if len(state) == num - 1:
 3         for pos in range(num):
 4             if not conflict(state, pos):
 5                 yield (pos,)
 6     else:
 7         for pos in range(num):
 8             if not conflict(state, pos):
 9                 for result in queens(num, state + (pos,)):
10                     yield (pos,) + result
11                 #state = state + (pos,)
12                 #queens(num, state)

不使用yield

 1 def queens(num, state):
 2     if len(state) == num - 1:
 3         tmp = []
 4         for pos in range(num):
 5             if not conflict(state, pos):
 6                 tmp.append((pos,))
 7         return tmp
 8     else:
 9         tmp = []
10         for pos in range(num):
11             if not conflict(state, pos):
12                 for result in queens(num, state + (pos,)):
13                     tmp.append((pos,) + result)
14         return tmp

测试

1 print list(queens(4, ()))

参考：

《python基础教程》人民邮电出版社