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.
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) {
* val = x;
* next = null;
* }
* }
*/
public class Solution {
public ListNode swapPairs(ListNode head) {
if(head==null||head.next==null)
return head;
ListNode faked=new ListNode(0);
faked.next=head;
ListNode pre=faked;
ListNode cur=head;
while(cur!=null&&cur.next!=null){
pre.next=cur.next;
cur.next=pre.next.next;
pre.next.next=cur;
pre=cur;
cur=pre.next;
}
return faked.next;
}
}