迭代和递归方法的运用

import randomdef prettyprint(solution):      #图形化处理数据    def line(pos,length=len(solution)):   #单行数据的处理        return '.'*(pos) + 'x'+'.'*(length-pos-1)    for pos in solution:       #画出每八行的图        print line(pos)def conflict(state,nextX):   #检测是否有冲突    nextY = len(state)    for i in range(nextY):        if abs(state[i]-nextX) in (0,nextY-i):  #按照距离进行比较            return True    return False #def queens(num,state):#    if len(state) == num-1:#        for pos in range(num):#            if not conflict(state,pos):#                yield posdef queens(num=8,state=()):    for pos in range(num):        print state        if not conflict(state,pos):            if len(state)==num-1:         #最后一个                yield (pos,)              #迭代方法            else:                for result in queens(num,state+(pos,)):   #递归前七个数据#                    print result                    yield(pos,)+resultprint 'bahuanghou'print list(queens(4))#for i in list(queens(8)):#    prettyprint(i)#    print 'next'#prettyprint(random.choice(list(queens(8))))