class Solution:

     # 返回合并后列表

     def Merge(self, pHead1, pHead2):

         # write code here

         if pHead1==None:

             return pHead2

         if pHead2==None:

             return pHead1

         head=ListNode(-1)

         head.next=None

         root=head

         while pHead1 is not None and pHead2 is not None:

             if pHead1.val<pHead2.val:

                 head.next=pHead1

                 head=pHead1

                 pHead1=pHead1.next

             else:

                 head.next=pHead2

                 head=pHead2

                 pHead2=pHead2.next

         if pHead1 is None:

             head.next=pHead2

         else:

             head.next=pHead1

         return root.next