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; } * } */ public class Solution { public ListNode swapPairs(ListNode head) { ListNode listNode = new ListNode(0); listNode.next = head; ListNode p1 = listNode; ListNode p2 = head; while (p2 != null && p2.next != null) { ListNode p3 = p2.next.next; p2.next.next = p2; p1.next = p2.next; p2.next = p3; p1 = p2; p2 = p2.next; } return listNode.next; } }