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 { /** * This is a fundamental problem.<br> * * @param head --The head node of the input linked list * @return head of the rotated linked list * @author Averill Zheng * @version 2014-06-03 * @since JDK 1.7 */ public ListNode swapPairs(ListNode head) { ListNode newHead = head; if(head != null && head.next != null){ ListNode currentNode = head; ListNode nextNode = currentNode.next; newHead = nextNode; currentNode.next = nextNode.next; nextNode.next = currentNode; ListNode previous = currentNode; currentNode = currentNode.next; while(currentNode != null && currentNode.next != null){ nextNode = currentNode.next; currentNode.next = nextNode.next; nextNode.next = currentNode; previous.next = nextNode; previous = currentNode; currentNode = currentNode.next; } } return newHead; } }