Initial data commit

Task/Display-a-linear-combination/Racket/display-a-linear-combination.rkt

@@ -0,0 +1,33 @@
+#lang racket/base
+(require racket/match racket/string)
+
+(define (linear-combination->string es)
+  (let inr ((es es) (i 1) (rv ""))
+    (match* (es rv)
+      [((list) "") "0"]
+      [((list) rv) rv]
+      [((list (? zero?) t ...) rv)
+       (inr t (add1 i) rv)]
+      [((list n t ...) rv)
+       (define ±n
+         (match* (n rv)
+           ;; zero is handled above
+           [(1 "") ""]
+           [(1 _) "+"]
+           [(-1 _) "-"]
+           [((? positive? n) (not "")) (format "+~a*" n)]
+           [(n _) (format "~a*" n)]))
+       (inr t (add1 i) (string-append rv ±n "e("(number->string i)")"))])))
+
+(for-each
+ (compose displayln linear-combination->string)
+ '((1 2 3)
+   (0 1 2 3)
+   (1 0 3 4)
+   (1 2 0)
+   (0 0 0)
+   (0)
+   (1 1 1)
+   (-1 -1 -1)
+   (-1 -2 0 -3)
+   (-1)))