八皇后问题

语言：python

# state[0] = 1 to represent a queen
# state = (1,3,0,2)
# * Q * *
# * * * Q 
# Q * * *
# * * Q *
def conflict(state, nextX):
    nextY = len(state)

    for i in range(nextY):
        if abs(state[i] - nextX) in (0, nextY - i):
            return True

    return False

使用yield

def queens(num, state):
    if len(state) == num - 1:
        for pos in range(num):
            if not conflict(state, pos):
                yield (pos,)
    else:
        for pos in range(num):
            if not conflict(state, pos):
                for result in queens(num, state + (pos,)):
                    yield (pos,) + result
                #state = state + (pos,)
                #queens(num, state)

不使用yield

def queens(num, state):
    if len(state) == num - 1:
        tmp = []
        for pos in range(num):
            if not conflict(state, pos):
                tmp.append((pos,))
        return tmp
    else:
        tmp = []
        for pos in range(num):
            if not conflict(state, pos):
                for result in queens(num, state + (pos,)):
                    tmp.append((pos,) + result)
        return tmp

测试

print list(queens(4, ()))

 参考：

《python基础教程》 人民邮电出版社