链表问题---反转单向和双向链表

【题目】

　　分别实现反转单向链表和反转双向链表的函数。
　　要求，时间复杂度O(N)，空间复杂度O(1)。

【代码实现】

#python3.5def reverseList(head):    if head == None:        return    pre = None    while head != None:        next = head.next        head.next = pre        pre = head        head = next    return predef reverseDoubleList(head):    if head == None:        return    pre = None    while head != None:        next = head.next        head.next = pre        head.pre = next        pre = head        head = next    return pre