Swap Nodes in Pairs

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.

public class Solution {
    public ListNode swapPairs(ListNode head) {
        if(head == null || head.next == null)
        {
            return head;
        }
        ListNode point = new ListNode(0);
        point.next = head;
        head = point;
        while(point.next != null && point.next.next != null)
        {
            ListNode temp = point.next.next.next;
            point.next.next.next = point.next;
            point.next = point.next.next;
            point.next.next.next = temp;
            point = point.next.next;
        }
        return head.next;
    }
}