Swap Two Nodes in Linked List

 1 /**
 2  * Definition for singly-linked list.
 3  * public class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int x) { val = x; }
 7  * }
 8  */
 9 public class Solution {
10     /**
11      * @param head a ListNode
12      * @oaram v1 an integer
13      * @param v2 an integer
14      * @return a new head of singly-linked list
15      */
16     public ListNode swapNodes(ListNode head, int v1, int v2) {
17         if (head == null) return null;
18         if (v1 == v2) return head;
19         
20         int dummyValue = Math.abs(v1) + Math.abs(v2) + 1;
21         
22         ListNode dummyHead = new ListNode(dummyValue);
23         dummyHead.next = head;
24         ListNode node1Parent = findNodeParent(dummyHead, v1);
25         ListNode node2Parent = findNodeParent(dummyHead, v2);
26         // if v1 or v2 doesn‘t exist, return
27         if (node1Parent == null || node2Parent == null) return head;
28         
29         ListNode node1 = node1Parent.next;
30         ListNode node2 = node2Parent.next;
31         // special case
32         if (node1.next == node2) {
33             node1Parent.next = node2;
34             node1.next = node2.next;
35             node2.next = node1;
36         } else if (node2.next == node1) {  // special case
37             node2Parent.next = node1;
38             node2.next = node1.next;
39             node1.next = node2;
40         } else {
41             ListNode temp = node2.next;
42             node2.next = node1.next;
43             node1.next = temp;
44             node1Parent.next = node2;
45             node2Parent.next = node1;
46         }
47         return dummyHead.next;
48     }
49     
50     private ListNode findNodeParent(ListNode head, int v1) {
51         while (head.next != null) {
52             if (head.next.val == v1) {
53                 return head;
54             } else {
55                 head = head.next;
56             }
57         }
58         return null;
59     }
60 }