add day 4 solutions

1 files changed, 27 insertions, 0 deletions

diff --git a/4.scm b/4.scm
new file mode 100755
index 0000000..668289a
--- /dev/null
+++ b/4.scm
@@ -0,0 +1,27 @@
+#!/usr/bin/env -S guile -s
+!#
+(use-modules (ice-9 regex)
+             (ice-9 textual-ports)
+             (srfi srfi-1))
+
+(define (read-lines port)
+  (letrec ((loop (lambda (l ls)
+                   (if (eof-object? l)
+                       ls
+                       (loop (get-line port) (cons l ls))))))
+    (reverse (loop (get-line port) '()))))
+
+(define (split-up nums)
+  (filter (lambda (x) (not (string-null? x))) (string-split nums char-set:whitespace)))
+
+(define (score line)
+  (let* ((m (string-match ": ([0-9| ]+) \\| ([0-9| ]+)" line))
+         (winning (split-up (match:substring m 1)))
+         (have (split-up (match:substring m 2)))
+         (shared (filter (lambda (x) (member x winning)) have)))
+    (if (null? shared) 0 (expt 2 (- (length shared) 1)))))
+
+(let* ((port (open-input-file "4.txt"))
+       (lines (read-lines port)))
+  (close-port port)
+  (display (fold + 0 (map score lines))))