From 9af65c8ac721024d0e45a2a6bde5c3f9fe638516 Mon Sep 17 00:00:00 2001
From: Charles <sircharlesaze@gmail.com>
Date: Tue, 7 Apr 2020 17:20:43 +0200
Subject: problem 1 2 4 in common lisp

---
 "lisp/\"asdf"                            |  0
 lisp/001-multiples_of_3_and_5.lisp       | 16 ++++++++++++++++
 lisp/002-even_fibonacci_numbers.lisp     | 24 ++++++++++++++++++++++++
 lisp/003-largest_prime_factor.lisp       | 31 +++++++++++++++++++++++++++++++
 lisp/004-largest_palindrome_product.lisp | 23 +++++++++++++++++++++++
 lisp/005-smallest_multiple.lisp          |  8 ++++++++
 6 files changed, 102 insertions(+)
 create mode 100644 "lisp/\"asdf"
 create mode 100644 lisp/001-multiples_of_3_and_5.lisp
 create mode 100644 lisp/002-even_fibonacci_numbers.lisp
 create mode 100644 lisp/003-largest_prime_factor.lisp
 create mode 100644 lisp/004-largest_palindrome_product.lisp
 create mode 100644 lisp/005-smallest_multiple.lisp

(limited to 'lisp')

diff --git "a/lisp/\"asdf" "b/lisp/\"asdf"
new file mode 100644
index 0000000..e69de29
diff --git a/lisp/001-multiples_of_3_and_5.lisp b/lisp/001-multiples_of_3_and_5.lisp
new file mode 100644
index 0000000..05b9173
--- /dev/null
+++ b/lisp/001-multiples_of_3_and_5.lisp
@@ -0,0 +1,16 @@
+;;;; ;;;;;;;;
+;;;; Multiples of 3 and 5
+;;;; Problem 1
+;;;;
+;;;; If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
+;;;; Find the sum of all the multiples of 3 or 5 below 1000.
+;;;; ;;;;;;;;
+
+(defvar *sum* 0)
+
+(dotimes (x 1000)
+  (when (or (eql 0 (mod x 5)) (eql 0 (mod x 3)))
+    (incf *sum* x)))
+
+(print *sum*)
+
diff --git a/lisp/002-even_fibonacci_numbers.lisp b/lisp/002-even_fibonacci_numbers.lisp
new file mode 100644
index 0000000..be9ed74
--- /dev/null
+++ b/lisp/002-even_fibonacci_numbers.lisp
@@ -0,0 +1,24 @@
+;;;; ;;;;;;;;
+;;;; Even Fibonacci numbers
+;;;; Problem 2
+;;;;
+;;;; Each new term in the Fibonacci sequence is generated by adding the previous two terms.
+;;;; By starting with 1 and 2, the first 10 terms will be:
+;;;; 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
+;;;; By considering the terms in the Fibonacci sequence whose values do not exceed four million,
+;;;; find the sum of the even-valued terms.
+;;;; ;;;;;;;;
+
+(defun sum (xs)
+  (if (null xs)
+    0
+    (+ (car xs) (sum (cdr xs)))))
+
+(defun fib (x y)
+  (when (> x 4000000) (return-from fib ()))
+  (cons x (fib y (+ x y))))
+
+(defvar *fibs-below-4m* (fib 1 2))
+
+(setf *fibs-below-4m* (remove-if-not #'evenp *fibs-below-4m*))
+(print (sum *fibs-below-4m*))
diff --git a/lisp/003-largest_prime_factor.lisp b/lisp/003-largest_prime_factor.lisp
new file mode 100644
index 0000000..e2fbe7a
--- /dev/null
+++ b/lisp/003-largest_prime_factor.lisp
@@ -0,0 +1,31 @@
+;;;; ;;;;;;;;
+;;;; Largest prime factor
+;;;; Problem 3
+;;;;
+;;;; The prime factors of 13195 are 5, 7, 13 and 29.
+;;;; What is the largest prime factor of the number 600851475143 ?
+;;;; ;;;;;;;;
+
+(defconstant +big-num+ 600851475143)
+
+(defun is-prime-rec (n d)
+(cond
+  ((= 0 (mod n d)) nil)
+  ((= 0 (mod n (+ d 2))) nil)
+  ((> (* d d) n) t)
+  (t (is-prime-rec n (+ d 6)))))
+
+(defun is-prime (n)
+  (when (or (= 0 (mod n 2)) (= 0 (mod n 3))) (return-from is-prime nil))
+  (is-prime-rec n 5))
+
+
+; (print (is-prime 1597))
+
+(defvar *largest* 0)
+
+(dotimes (x +big-num+)
+  (print x)
+  (when (and (= 0 (mod +big-num+ is-prime x) (setf *largest* x)))
+
+(print *largest*)
diff --git a/lisp/004-largest_palindrome_product.lisp b/lisp/004-largest_palindrome_product.lisp
new file mode 100644
index 0000000..8cbc7c9
--- /dev/null
+++ b/lisp/004-largest_palindrome_product.lisp
@@ -0,0 +1,23 @@
+;;;; ;;;;;;;;
+;;;; Largest palindrome product
+;;;; Problem 4
+;;;;
+;;;; A palindromic number reads the same both ways.
+;;;; The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.
+;;;; Find the largest palindrome made from the product of two 3-digit numbers.
+;;;; ;;;;;;;;
+
+(defun palindrome-p (n)
+  (equal (write-to-string n) (reverse (write-to-string n))))
+
+(print (palindrome-p 32))
+
+(defvar *largest* 0)
+
+(loop :for x :from 999 :downto 1 :do
+      (loop :for y :from 999 :downto 1 :do
+            (when (and (palindrome-p (* x y)) (> (* x y) *largest*))
+              (print (* x y))
+              (setf *largest* (* x y)))))
+
+(print *largest*)
diff --git a/lisp/005-smallest_multiple.lisp b/lisp/005-smallest_multiple.lisp
new file mode 100644
index 0000000..9599507
--- /dev/null
+++ b/lisp/005-smallest_multiple.lisp
@@ -0,0 +1,8 @@
+;;;; ;;;;;;;;
+;;;; Smallest multiple
+;;;; Problem 5
+;;;; 
+;;;; 2520 is the smallest number that can be divided by each of the numbers from 1 to 10 without any remainder.
+;;;; What is the smallest positive number that is evenly divisible by all of the numbers from 1 to 20?
+;;;; ;;;;;;;;
+
-- 
cgit