euler problem 004 in lisp

master
Evan Hemsley 2016-10-21 09:52:08 -07:00
parent 1d2e635f05
commit b3d28777fd
2 changed files with 55 additions and 0 deletions

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@ -2,6 +2,7 @@
(defun sum (list) (apply '+ list)) (defun sum (list) (apply '+ list))
(defun select (expr list) (remove-if-not expr list)) (defun select (expr list) (remove-if-not expr list))
(defun filter (expr list) (remove-if expr list)) (defun filter (expr list) (remove-if expr list))
(defun empty (list) (eq list nil))
(defun partial (func &rest args1) (defun partial (func &rest args1)
(lambda (&rest args2) (lambda (&rest args2)
@ -11,3 +12,48 @@
(defun prime (n) (defun prime (n)
(eq (length (member T (mapcar (lambda (a) (eq (mod n a) 0)) (range 2 (sqrt n))))) 0) (eq (length (member T (mapcar (lambda (a) (eq (mod n a) 0)) (range 2 (sqrt n))))) 0)
) )
(defun cartesian-helper (thing list)
(if (empty list)
nil
(cons (list thing (first list)) (cartesian-helper thing (rest list)))
)
)
(defun cartesian (list-one list-two)
(if (empty list-one)
nil
(append (cartesian-helper (first list-one) list-two) (cartesian (rest list-one) list-two))
)
)
(defun number-to-digit-list (num)
(if (< num 10)
(list num)
(append (number-to-digit-list (floor (/ num 10))) (list (mod num 10)))
)
)
(defun digit-list-to-number (digit-list)
(if (empty digit-list)
0
(+ (* (first digit-list) (expt 10 (- (length digit-list) 1))) (digit-list-to-number (rest digit-list)))
)
)
(defun is-palindrome (num)
(let* ((digit-list (number-to-digit-list num)))
(equal (reverse digit-list) digit-list))
)
(defun resolve-tuple (expr tuple)
(funcall expr (first tuple) (second tuple))
)
(defun resolve-tuples (expr tuple-list)
(mapcar (partial #'resolve-tuple expr) tuple-list)
)
(defun max-of (list)
(reduce #'max list)
)

9
lisp/euler004.lisp Normal file
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@ -0,0 +1,9 @@
(load "euler.lisp")
(defun three-digit-products ()
(resolve-tuples (lambda (a b) (* a b)) (cartesian (range 100 999) (range 100 999)))
)
(defun solution ()
(max-of (select #'is-palindrome (three-digit-products)))
)