LeetCode 21 -- Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

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  public ListNode mergeTwoLists(ListNode l1, ListNode l2) {

         ListNode p1 = l1;
         ListNode p2 = l2;

         ListNode fakeHead = new ListNode(0);
         ListNode p = fakeHead;

         while(p1 != null && p2 != null){
           if(p1.val <= p2.val){
               p.next = p1;
               p1 = p1.next;
           }else{
               p.next = p2;
               p2 = p2.next;
           }

           p = p.next;
         }

         if(p1 != null)
             p.next = p1;
         if(p2 != null)
             p.next = p2;

         return fakeHead.next;
     }

重点是next边界的使用，注意一点 最好使用新指针 不要改动原有的东西。