【发布时间】:2013-05-11 11:26:19
【问题描述】:
我很难完全理解 CL 的 Loop 宏。 这是我的 Project Euler Nr 的代码。 32:
(defun number-to-list (nr)
(map 'list #'digit-char-p (prin1-to-string nr)))
(defun nine-digits-p (multiplicand multiplier )
(= (length (equationlist multiplicand multiplier
(* multiplicand multiplier))) 9))
(defun equationlist (multiplicand multiplier product)
(append (number-to-list multiplicand) (number-to-list multiplier)
(number-to-list product)))
(defun pandigital (multiplicand multiplier)
(equal (sort (equationlist multiplicand multiplier
(* multiplicand multiplier)) #'<)
'(1 2 3 4 5 6 7 8 9)))
(defun pandigital-list ()
(loop
for i from 1 to 2000 collect
(loop for j from 2 to 2000
when (and (nine-digits-p i j) (pandigital i j)) collect (* i j))))
(defun euler-32 ()
(reduce #'+ (reduce #'union (pandigital-list))))
虽然这给了我正确的解决方案,但我的问题在于函数“pandigital-list”。它不是只收集泛数字,而是返回一个包含“NIL”和少数正确数字的列表。
如何更改此函数以仅返回我感兴趣的数字?
【问题讨论】:
标签: lisp common-lisp