24. Swap Nodes in Pairs leetcode Python 2016 new Season

Given a linked list, swap every two adjacent nodes and return its head.
For example,

Given 

1->2->3->4

, you should return the list as 

2->1->4->3

.
Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed.

Show Company Tags

Show Tags

Show Similar Problems

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
def swapPairs(self, head):
"""
:type head: ListNode
:rtype: ListNode
"""
if not head or not head.next:
return head
dummyHead = pNode = ListNode(None)
pNode.next = head
while pNode.next and pNode.next.next:
tmp = pNode.next.next
pNode.next.next = tmp.next
tmp.next = pNode.next
pNode.next = tmp
pNode = pNode.next.next
return dummyHead.next