# 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
"""
dummy = ListNode(0)
dummy.next = head
dummy.next = self.recursive(head)
return dummy.next
def recursive(self, node):
if node == None or node.next == None:
return node
p = node.next
node.next = self.recursive(p.next)
p.next = node
return p
# 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
"""
dummy = ListNode(0)
dummy.next = head
prev = dummy
p = dummy.next
while p != None and p.next != None:
n = p.next
nn = n.next
prev.next = n
n.next = p
p.next = nn
prev = p
p = nn
return dummy.next
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.