[FP/HW1] Reworked almost all functions for exercise 2

1 files changed, 31 insertions, 30 deletions

diff --git a/Year 2/Functional Programming/hw1.rkt b/Year 2/Functional Programming/hw1.rkt
index 3f78abd..548e441 100644
--- a/Year 2/Functional Programming/hw1.rkt
+++ b/Year 2/Functional Programming/hw1.rkt
@@ -18,40 +18,41 @@
 
 ;;; Задача 2
 
-(define (swap-last2-digits n)
-  (+ (* (quotient n 100) 100)
-     (* (remainder n 10) 10)
-     (quotient (remainder n 100) 10)))
-
-(define (rotate-left n)
-  (if (<= n 9)
-    n
-    (swap-last2-digits (+ (* (rotate-left (quotient n 10)) 10)
-                          (remainder n 10)))))
-
-(define (pow10 n)
-  (if (= n 0)
-    1
-    (* 10 (pow10 (sub1 n)))))
+(define (^10 n)
+  (define (calc-iter n val)
+    (if (= n 0)
+      val
+      (calc-iter (sub1 n) (* val 10))))
+  (calc-iter n 1))
 
 (define (numlen n)
-  (if (= n 0)
-    0
-    (add1 (numlen (quotient n 10)))))
+  (define (calc-iter n len)
+    (if (= n 0)
+      len
+      (calc-iter (quotient n 10) (add1 len))))
+  (calc-iter n 0))
+
+(define (rotate-left n)
+  (define 10^len-1 (^10 (sub1 (numlen n))))
+  (+ (* (remainder n 10^len-1) 10) ; всичко без най-дясната цифра
+     (quotient n 10^len-1)))       ; най-дясната цифра
 
 (define (rotate-left-preserved n d)
-  (define pbl (pow10 (- (numlen n) d)))
-  (+ (* (quotient n pbl) pbl)
-     (if (< (remainder n pbl) pbl)
-       (* (rotate-left (remainder n pbl)) 10)
-       (rotate-left (remainder n pbl)))))
+  (define 10^rotatelen (^10 (- (numlen n) d)))
+  (define to-rotate (remainder n 10^rotatelen))
+  (if (<= n 9)
+    n
+    (+ (- n to-rotate) ; запазените цифри са запазени, другите са нули
+       (if (< to-rotate (quotient 10^rotatelen 10)) ; ако to-rotate "започва" с нули
+         (- (rotate-left (+ to-rotate 10^rotatelen)) 1) ; "долепяме" 1ца до левия край временно, за да може да се звърти
+         (rotate-left to-rotate)))))
 
 (define (max-rot n)
-  (define nrlen (sub1 (numlen n)))
-  (define (helper i current biggest)
-    (if (>= i nrlen)
+  (define len-1 (sub1 (numlen n)))
+  (define (calc-iter preserved current biggest)
+    (if (= preserved len-1) ; при равенство ще има само една цифра която ще може да бъде завъртяна
       biggest
-      (helper (add1 i)
-              (rotate-left-preserved current (add1 i))
-              (if (> current biggest) current biggest))))
-  (helper 0 (rotate-left n) 0))
+      (calc-iter (add1 preserved)
+                 (rotate-left-preserved current (add1 preserved))
+                 (if (> current biggest) current biggest))))
+  (calc-iter 0 (rotate-left n) 0))