I created only one dummy node at the beginning to save myself many 'if' conditions.
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
ListNode list1Cursor = l1;
ListNode list2Cursor = l2;
ListNode currentNode = new ListNode(-1); // Dummy node
ListNode head = currentNode;
while (list1Cursor != null && list2Cursor != null)
{
if (list1Cursor.val < list2Cursor.val) {
currentNode.next = list1Cursor;
list1Cursor = list1Cursor.next;
currentNode = currentNode.next;
} else {
currentNode.next = list2Cursor;
list2Cursor = list2Cursor.next;
currentNode = currentNode.next;
}
}
// Complete the rest
while (list1Cursor != null) {
currentNode.next = list1Cursor;
currentNode = currentNode.next;
list1Cursor = list1Cursor.next;
}
while (list2Cursor != null) {
currentNode.next = list2Cursor;
currentNode = currentNode.next;
list2Cursor = list2Cursor.next;
}
return head.next;
}