fix: optimize sliding

Author: walking-octopus

main.rkt

@@ -102,16 +102,18 @@
 
 
 (define (sliding lst size [step 1])
-  (define (tail-call lst)
-    (if (>= size (length lst))
-        (list lst)
-        (cons (take lst size)
-              (tail-call (drop lst step)))))
-  (cond
-    [(> step (length lst))
-      (error "step has to be equal to or smaller than length of the list")]
-    [(= step (length lst)) (list lst)]
-    [else (tail-call lst)]))
+  (when (> step (length lst))
+    (error "step has to be equal to or smaller than length of the list"))
+
+  (cond [(= step (length lst))
+         (list lst)]
+        [(let recur ([lst lst]
+                     [len (length lst)])
+         (if (>= size len)
+             (if (empty? lst) empty (list lst))
+                 (cons (take lst size)
+                       (recur (drop lst step)
+                              (- len step)))))]))
 
 
 (define (scanl proc lst)