给定链表L0->L1->...L(n-1)->Ln,把它重新排序为L0->Ln->L1->L(n-1)->L2->L(n-2)...

给定链表L0->L1->…L(n-1)->Ln,把它重新排序为L0->Ln->L1->L(n-1)->L2->L(n-2)…要求（1）在原来链表基础上进行排序，不能申请新节点（2）只能修改节点next域，不能修改数据域

class LNode:
    def __init__(self,x=None):
        self.data=x
        self.next=None

def FindMiddleNode(head):
    #查找链表中间节点并断开
    if head is None or head.next is None:
        slow_next = head
        return  slow_next
    else:
        slow = head
        fast = head
        slow_next = head
        while fast is not None and fast.next is not None:
            slow = slow.next #慢指针走一步
            fast = fast.next.next#快指针走两步
            slow_next = slow.next
        slow.next = None #断开指针
    return slow_next

def Reverse(head):
    #对不带头节点的单链表翻转
    if head is None or head.next is None:
        return head
    pre = head
    cur = head.next
    pre.next = None
    while cur is not None:
        next = cur.next
        cur.next &