list - 检查对角线时出现逻辑错误 - nQueens

Question

在用 values-list 解决了我的错误并能够运行我的程序直到结束后，我发现我的对角线检查似乎有逻辑错误。我的输入如下:

(威胁？'(1 3)'((1 0)(2 4)(3 0)(4 0)(5 0)(6 0)(7 0)(8 0)))

第一个参数是我们正在测试的棋盘空间是否可以放置女王，第二个参数是棋盘的状态，y 值 1-8 决定棋子的列位置，0 值将表示 x 值行将不包含任何部分。我的代码如下:

(defun diagonal(point1 point2)
    (= (abs (- ( car point1 ) ( car point2 )))
       (abs (- ( cadr point1 ) ( cadr point2 ))))
)

(defun THREAT?(x y)
    ; Checks threat on the vertical
    (when (not (eq (values-list (cdr (nth (- (car x) 1 ) y )) ) '0 ) )
            (return-from THREAT? t)
    )
    (loop for i from 0 to (list-length y)

            ; Checks threat on the horizontal
            when (eq (values-list ( cdr x  )) (values-list (cdr (nth i y))) )
                    do (return-from THREAT? t)
            ; With the help of the diagonal function checks along the diagonal
            when (diagonal x (nth i y) )
                    do (return-from THREAT? t)
    )
)

如果我的理解是正确的，我的程序应该循环遍历 y 的每个元素。它会将 x 和当前 y 对传递给对角线函数。对角线函数将减去两个和它们的绝对值并检查它们是否相等(如果它们是对角线那么它们应该是例如(1 2)和(2 3)是对角线因此|1 - 2| = 1和| 2 - 3| = 1).如果这些数字相等，则对角线函数应返回 true。相应的 when 语句应该只在它从对角线函数接收到 true 时激活，但它似乎总是返回 true，即使我给程序一个完全空白的板。如何修复对角线以正确确定棋盘上的威胁？非常感谢任何帮助!

Answer 1

我已将您的代码重写为更好的 Lisp 风格。

• 更好的命名。
• 具有有用名称的过程使注释变得多余
• 单个程序更易于测试
• 摆脱了 VALUES-LIST 废话
• 去除所有 CAR、CDR、CADR。使用 FIRST 和 SECOND。
• 为点的 x 和 y 分量引入了访问器
• 用 RETURN-FROM 摆脱了奇怪的控制流，用简单的 OR 代替了它
• 实际上直接遍历一个列表，而不是一直使用 NTH
• EQ不是用来比较数字相等的，用=代替
• 不要将括号单独放在一行中。
• 正确缩进和格式化代码
• 不要在括号之间放置空格
• 在原子和左括号之间放置一个空格

代码:

(defun get-x (point)
  (first point))

(defun get-y (point)
  (second point))

(defun diagonal? (point1 point2)
  (= (abs (- (get-x point1) (get-x point2)))
     (abs (- (get-y point1) (get-y point2)))))

(defun vertical? (point)
  (not (zerop (get-y point))))

(defun horizontal? (point1 point2)
  (= (get-y point1)
     (get-y point2)))

(defun threat? (point list-of-columns)
  (or (vertical? (nth (1- (get-x point)) list-of-columns))
      (loop for point2 in list-of-columns
            when (or (horizontal? point point2)
                     (diagonal?   point point2))
            return t)))

示例

现在我们可以追踪三个威胁谓词:

? (trace vertical? diagonal? horizontal?)
NIL

现在你可以调用你的例子了:

? (threat? '(1 3) '((1 0) (2 4) (3 0) (4 0) (5 0) (6 0) (7 0) (8 0)))
0> Calling (VERTICAL? (1 0)) 
<0 VERTICAL? returned NIL
0> Calling (HORIZONTAL? (1 3) (1 0)) 
<0 HORIZONTAL? returned NIL
0> Calling (DIAGONAL? (1 3) (1 0)) 
<0 DIAGONAL? returned NIL
0> Calling (HORIZONTAL? (1 3) (2 4)) 
<0 HORIZONTAL? returned NIL
0> Calling (DIAGONAL? (1 3) (2 4)) 
<0 DIAGONAL? returned T
T

这应该有所帮助，以便您可以更好地调试代码...查看跟踪输出。

不使用空列描述的版本

(defun get-x (point)
  (first point))

(defun get-y (point)
  (second point))

(defun diagonal? (point1 point2)
  (= (abs (- (get-x point1) (get-x point2)))
     (abs (- (get-y point1) (get-y point2)))))

(defun vertical? (point list-of-columns)
  (let ((point2 (find (get-x point) list-of-columns :key #'get-x)))
    (and point2 (not (zerop (get-y point2))))))

(defun horizontal? (point1 point2)
  (= (get-y point1)
     (get-y point2)))

(defun threat? (point list-of-columns)
  (or (vertical? point list-of-columns)
      (loop for point2 in list-of-columns
            when (or (horizontal? point point2)
                     (diagonal?   point point2))
            return t)))

(defun print-board (board)
  (format t "~%+-+-+-+-+-+-+-+-+")
  (dotimes (y 8)
    (terpri)
    (dotimes (x 8)
      (format t "|~a" (if (member (list x y) board :test #'equal) "x" " ")))
    (format t "|~%+-+-+-+-+-+-+-+-+")))

例子:

CL-USER 138 > (threat? '(1 2) '((2 4)))
NIL

CL-USER 139 > (print-board '((1 2) (2 4)))

+-+-+-+-+-+-+-+-+
| | | | | | | | |
+-+-+-+-+-+-+-+-+
| | | | | | | | |
+-+-+-+-+-+-+-+-+
| |x| | | | | | |
+-+-+-+-+-+-+-+-+
| | | | | | | | |
+-+-+-+-+-+-+-+-+
| | |x| | | | | |
+-+-+-+-+-+-+-+-+
| | | | | | | | |
+-+-+-+-+-+-+-+-+
| | | | | | | | |
+-+-+-+-+-+-+-+-+
| | | | | | | | |
+-+-+-+-+-+-+-+-+
NIL

另一个例子:

CL-USER 140 > (threat? '(1 2) '((2 4) (4 5)))
T

CL-USER 141 > (print-board '((1 2) (2 4) (4 5)))

+-+-+-+-+-+-+-+-+
| | | | | | | | |
+-+-+-+-+-+-+-+-+
| | | | | | | | |
+-+-+-+-+-+-+-+-+
| |x| | | | | | |
+-+-+-+-+-+-+-+-+
| | | | | | | | |
+-+-+-+-+-+-+-+-+
| | |x| | | | | |
+-+-+-+-+-+-+-+-+
| | | | |x| | | |
+-+-+-+-+-+-+-+-+
| | | | | | | | |
+-+-+-+-+-+-+-+-+
| | | | | | | | |
+-+-+-+-+-+-+-+-+
NIL