emmmmmm 22题括号生成，想了想思路，感觉如果用别的语言特别容易就写出来了，但是用python的话，emmm，暂时有点不想写，哈哈哈，罢了，改日再做，略过略过。。。
这道题很简单啊，10分钟也没用，一次就ac了。
就是简单的节点交换而已。
# Definition for singly-linked list.
class ListNode:def __init__(self, x):self.val = xself.next = Nonedef swapPairs(head):if head == None or head.next == None:return headi = headj = head.nexti_pre = heady = headwhile i != None and j != None:if i == head:i.next = j.nextj.next = iy = ji_pre = iif i.next != None and j.next.next.next != None:i = i.nextj = j.next.next.nextelse:return yelse:i.next = j.nextj.next = ii_pre.next = ji_pre = iif i.next != None and j.next.next.next != None:i = i.nextj = j.next.next.nextelse:return yreturn yn = ListNode(1)
n.next = ListNode(2)
n.next.next = ListNode(3)
n.next.next.next = ListNode(4)p = swapPairs(n)
while p != None:print(p.val)p = p.next