update

Task/Permutations/Racket/permutations.rkt

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+#lang racket
+
+;; using a builtin
+(permutations '(A B C))
+;; -> '((A B C) (B A C) (A C B) (C A B) (B C A) (C B A))
+
+;; a random simple version (which is actually pretty good for a simple version)
+(define (perms l)
+  (let loop ([l l] [tail '()])
+    (if (null? l) (list tail)
+        (append-map (λ(x) (loop (remq x l) (cons x tail))) l))))
+(perms '(A B C))
+;; -> '((C B A) (B C A) (C A B) (A C B) (B A C) (A B C))