Add (net ricketyspace sicp two nineteen).

1 files changed, 26 insertions, 0 deletions

diff --git a/net/ricketyspace/sicp/two/nineteen.scm b/net/ricketyspace/sicp/two/nineteen.scm
new file mode 100644
index 0000000..e4f7259
--- /dev/null
+++ b/net/ricketyspace/sicp/two/nineteen.scm
@@ -0,0 +1,26 @@
+;;;; License: CC0-1.0
+
+(define-module (net ricketyspace sicp two nineteen)
+  #:export (us-coins uk-coins cc))
+
+(define us-coins (list 50 25 10 5 1))
+(define uk-coins (list 100 50 20 10 5 2 1 0.5))
+
+(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)))))
+
+(define (no-more? coin-values)
+  (null? coin-values))
+
+(define (except-first-denomination coin-values)
+  (cdr coin-values))
+
+(define (first-denomination coin-values)
+  (car coin-values))