/**

• Definition for singly-linked list.

• public class ListNode {

• int val;

• ListNode next;

• ListNode() {}

• ListNode(int val) { this.val = val; }

• ListNode(int val, ListNode next) { this.val = val; this.next = next; }

• }
  */
  class Solution {
  public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
  if (list1 == null)
  return list2;
  if (list2 == null)
  return list1;

   ListNode temp = new ListNode(-1);
   ListNode ptr = temp;
   while (list1 != null && list2 != null)
   {
       if (list1.val < list2.val)
       {
           ptr.next = list1;
           list1 = list1.next;
       }
       else
       {
           ptr.next = list2;
           list2 = list2.next;
       }
       ptr = ptr.next;
   }
   
   while (list1 != null)
   {
       ptr.next = list1;
       ptr = ptr.next;
       list1 = list1.next;
   }
   
   while (list2 != null)
   {
       ptr.next = list2;
       ptr = ptr.next;
       list2 = list2.next;
   }
   
   return temp.next;

  }
  }