sliding-window

#lang racket
(require test-engine/racket-tests)


(define (rotations lst)
  (letrec ((go (λ (n acc)
    (if (= n 0) acc
        (go (sub1 n) (let ((c (car acc)))
                       `(,`(,@(cdr c) ,(car c)) ,@acc)))))))
  (reverse (go (length lst) (list lst)))))

(define (sliding-window n lst)
  (apply map list (take (rotations lst) n)))

(check-expect (sliding-window 3 `(1 2 3 4 5)) `((1 2 3) (2 3 4) (3 4 5) (4 5 1) (5 1 2)))
(test)