Merge pull request #34 from wobh/difference-of-squares

xlisp #23: Difference of squares

config.json

@@ -20,7 +20,8 @@
     "anagram",
     "nucleotide-count",
     "meetup",
-    "triangle"
+    "triangle",
+    "difference-of-squares"
   ],
   "deprecated": [
 

difference-of-squares/difference-of-squares-test.lisp

@@ -0,0 +1,33 @@
+(ql:quickload "lisp-unit")
+
+(defpackage #:squares-test
+  (:use #:cl #:lisp-unit))
+
+(load "squares")
+
+(in-package #:squares-test)
+
+(define-test square-of-sums-to-5
+  (assert-equal 225 (squares:square-of-sums 5)))
+(define-test sum-of-squares-to-5
+  (assert-equal 55 (squares:sum-of-squares 5)))
+(define-test difference-of-sums-to-5
+  (assert-equal 170 (squares:difference 5)))
+
+(define-test square-of-sums-to-10
+  (assert-equal 3025 (squares:square-of-sums 10)))
+(define-test sum-of-squares-to-10
+  (assert-equal 385 (squares:sum-of-squares 10)))
+(define-test difference-of-sums-to-10
+  (assert-equal 2640 (squares:difference 10)))
+
+(define-test square-of-sums-to-100
+  (assert-equal 25502500 (squares:square-of-sums 100)))
+(define-test sum-of-squares-to-100
+  (assert-equal 338350 (squares:sum-of-squares 100)))
+(define-test difference-of-sums-to-100
+  (assert-equal 25164150 (squares:difference 100)))
+
+(let ((*print-errors* t)
+      (*print-failures* t))
+  (run-tests :all :squares-test))

difference-of-squares/example.lisp

@@ -0,0 +1,17 @@
+(defpackage #:squares
+  (:use #:cl)
+  (:export #:sum-of-squares
+           #:square-of-sums
+           #:difference))
+
+(in-package #:squares)
+
+(defun square-of-sums (n)
+  (expt (* 1/2 n (1+ n)) 2))
+
+(defun sum-of-squares (n)
+  (* 1/6 n (1+ n) (1+ (* 2 n))))
+
+(defun difference (n)
+  (- (square-of-sums n)
+     (sum-of-squares n)))

difference-of-squares/squares.lisp

@@ -0,0 +1,7 @@
+(defpackage #:squares
+  (:use #:cl)
+  (:export #:sum-of-squares
+           #:square-of-sums
+           #:difference))
+
+(in-package #:squares)