Question

我是Lisp的新手，我需要创建函数，而不是返回包含特殊数字的子列表的第二个值。

例如，我有两个参数的函数：其中一个是带有子列表的列表，第二个是我要搜索的特殊号码：

 (find_neighbours '((1 2) (3 1) (4 5) (9 1) (2 3) (1 5)) 1)

该函数应返回类似的内容：

(2 3 9 5)

因为我们在(1 2) (3 1) ...内有1个子列表。

这是我的解决方案：

(defun find_neighbours (lst node)
    (if lst
        (cond 
            ((= node (caar lst))  
                (cons (cadar lst) 
                (find_neighbours (cdr lst) node))
            )
            ((= node (cadar lst)) 
                (cons (caar  lst) 
                (find_neighbours (cdr lst) node))
            )
            (T (find_neighbours (cdr lst) node))
        )
    )
)

Answer 1

这是一个简单的方法：

(defun other-end (edge vertex)
  "Return the other end of the EDGE if VERTEX is one of them or NIL."
  (destructuring-bind (beg end) edge
    (cond ((= vertex beg) end)
          ((= vertex end) beg)
          (t nil))))

(defun neighbors (graph vertex)
  "Return the list of neighbors of the VERTEX in the GRAPH."
  (loop for edge in edges
    for other = (other-end edge vertex)
    when other collect other))

还有其他方法，例如，

(defun neighbors (graph vertex)
  "Return the list of neighbors of the VERTEX in the GRAPH."
  (delete nil (mapcar (lambda (edge) (other-end edge vertex))
                      graph)))

等...

Answer 2

我用这种方式解决了我的问题：

(defun find_neighbours (lst node)
    (if lst
        (cond 
            ((= node (caar lst))  
                (cons (cadar lst) 
                (find_neighbours (cdr lst) node))
            )
            ((= node (cadar lst)) 
                (cons (caar  lst) 
                (find_neighbours (cdr lst) node))
            )
            (T (find_neighbours (cdr lst) node))
        )
    )
)

获取Lisp中带有特殊编号的列表

2 个答案: