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.
func swapPairs(head *ListNode) *ListNode {
if head==nil{
return nil
}
if head.Next==nil{
return head
}
var ret*ListNode
if head.Next.Next==nil{
var p* ListNode=head
ret=p.Next
ret.Next=p
p.Next=nil
return ret
}
tmpret:=swapPairs(head.Next.Next)
var tmp *ListNode=head
ret=tmp.Next
ret.Next=tmp
tmp.Next=tmpret
return ret
}