ex2.19-change-count-revisit.scm

(define (count-change amount)
  (cc1 amount 5))
(define (cc1 amount kinds-of-coins)
  (cond ((= amount 0) 1)
	((or (< amount 0) (= kinds-of-coins 0)) 0)
	(else (+ (cc1 amount
		      (- kinds-of-coins 1))
		 (cc1 (- amount
			 (first-denomination kinds-of-coins))
		      kinds-of-coins)))))
(define (first-denomination kinds-of-coins)
  (cond ((= kinds-of-coins 1) 1)
	((= kinds-of-coins 2) 5)
	((= kinds-of-coins 3) 10)
	((= kinds-of-coins 4) 25)
	((= kinds-of-coins 5) 50)))

(count-change 100)


(define us-coins (list 50 25 10 5 1))
(define uk-coins (list 100 50 20 10 5 2 1 0.5))


(define first-denomination car)

(define except-first-denomination cdr)
(define no-more? null?)


(define (cc amount coin-values)
  (cond ((= amount 0) 1)
	((or (< amount 0) (no-more? coin-values)) 0)
	(else
	  (+ (cc amount
		 (except-first-denomination coin-values))
	     (cc (- amount
		    (first-denomination coin-values))
		 coin-values)))))


(cc 100 us-coins)

; The order doesn't matter because with the existence of condition:
; (cc amount (except-first-denomination coin-values))
; each denomination got the chance to be processed with initial amount
; since cc is resursive, so on so forth
;