Swap Nodes in Pairs

[ZhangQianXing]

if(head==null||head.next==null){
return head;
}
ListNode dummy=new ListNode(-1);
dummy.next=head;
ListNode pivot=dummy;
ListNode tail=dummy;
pivot=pivot.next;
while(pivot!=null){
ListNode temp=pivot.next;
if(pivot.next==null){
break;
}
pivot.next=pivot.next.next;
temp.next=null;
temp.next=pivot;
tail.next=temp;
tail=tail.next.next;
pivot=pivot.next;
}
return dummy.next;