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。