leetcode 【 Swap Nodes in Pairs 】python 实现

             1
            #
             Definition for singly-linked list.
             2
            #
             class ListNode:
             3
            #
                 def __init__(self, x):
             4
            #
                     self.val = x
             5
            #
                     self.next = None
             6
             7
            class
             Solution:

             8
            #
             @param a ListNode
             9
            #
             @return a ListNode
            10
            def
             swapPairs(self, head):

            11
            if head is None or head.next is None: 
12return head
1314         dummyhead = ListNode(0)
15         dummyhead.next = head
1617         pre = dummyhead
18         curr = head
19while curr isnot None and curr.next isnot None:
20             tmp = curr.next
21             curr.next = tmp.next
22             tmp.next = pre.next 
23             pre.next = tmp
24             pre = curr
25             curr = curr.next
26return dummyhead.next