day 2

1 files changed, 46 insertions, 0 deletions

diff --git a/02/2.scm b/02/2.scm
new file mode 100644
index 0000000..e7f9871
--- /dev/null
+++ b/02/2.scm
@@ -0,0 +1,46 @@
+(import (chicken string))
+(import (chicken io))
+(import (chicken sort))
+(import matchable)
+(import srfi-1)
+
+(define input
+  (with-input-from-file "input"
+    (lambda ()
+      (let loop ((ret '()))
+        (let ((line (read-line)))
+          (if (eof-object? line)
+              (reverse ret)
+              (loop (cons line ret))))))))
+
+(set! input (map string-split input))
+(set! input (map (lambda (lst) (map string->number lst)) input))
+
+(define (diff in)
+  (let loop ((lst in) (ret '()))
+    (match lst
+      ((a b . r) (loop (cdr lst) (cons (- a b) ret)))
+      ((a) (reverse ret)))))
+
+(define (same-sign? in)
+  (define prod (map (lambda (x) (* x (car in))) in))
+  (foldl (lambda (a b) (and a b)) #t (map (lambda (x) (> x 0)) prod)))
+
+(define (extend in)
+  (let loop ((lst in) (head '()) (ret '()))
+    (if (null? lst)
+        (cons in ret)
+        (loop (cdr lst)
+              (cons (car lst) head)
+              (cons (append (reverse head) (cdr lst)) ret)))))
+
+(define (ladder-safe? in)
+  (and (same-sign? in)
+       (not (any (lambda (x) (> (abs x) 3)) in))))
+
+(define (safe? in)
+  (any ladder-safe? (map diff (extend in))))
+
+(display (length (filter safe? input)))
+(newline)
+