我终于懂时间的重量：public static ListNode mergeTwoLists(ListNode l1, ListNode l2) { Deque<Integer> stack=new LinkedList<>(); while(l2!=null) { stack.push(l2.val); l2=l2.next; } ListNode ret=new ListNode(); ListNode head=ret; ListNode temp; while(l1!=null&&!stack.isEmpty()){ if(l1.val<=stack.peek()) { temp=new ListNode(l1.val); l1=l1.next; } else{ temp=new ListNode(stack.pop()); } head.next=temp; head=head.next; } while(l1!=null){ temp=new ListNode(l1.val); head.next=temp; head=head.next; } while(!stack.isEmpty()){ temp=new ListNode(stack.pop()); head.next=temp; head=head.next; } return ret.next; }