add day 3 solutions

1 files changed, 61 insertions, 0 deletions

diff --git a/3.scm b/3.scm
new file mode 100755
index 0000000..c43d0bd
--- /dev/null
+++ b/3.scm
@@ -0,0 +1,61 @@
+#!/usr/bin/env -S guile -s
+!#
+(use-modules (ice-9 regex)
+             (ice-9 textual-ports)
+             (srfi srfi-1))
+
+(define line-length 140) ;; nasty :(
+
+(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 (candidates-for-line line)
+  (letrec ((loop (lambda (l ls)
+                   (if (not l) ls
+                        (loop (string-match "[0-9]+" line (match:end l)) (cons l ls))))))
+    (loop (string-match "[0-9]+" line) '())))
+
+(define (find-candidates lines)
+  (let ((i -1))
+    (concatenate (map-in-order (lambda (line) (let ((cands (candidates-for-line line)))
+                                   (set! i (+ i 1))
+                                   (map (lambda (cand)
+                                          `(,i ,(match:start cand) ,(- (match:end cand) (match:start cand)) ,(string->number (match:substring cand)))) cands))) lines))))
+
+(define (saturating-add lhs rhs max)
+  (let ((res (+ lhs rhs)))
+    (if (> res max) max res)))
+
+(define (saturating-sub lhs rhs min)
+  (let ((res (- lhs rhs)))
+    (if (< res min) min res)))
+
+(define (contains-part-symbol? str)
+  (string-match "[^0-9|\\.]" str))
+
+(define (part-number? candidate lines)
+  (let ((above (substring (list-ref lines (saturating-sub (car candidate) 1 0))
+                          (saturating-sub (cadr candidate) 1 0)
+                          (saturating-add (+ (cadr candidate) (caddr candidate)) 1 line-length)))
+        (below (substring (list-ref lines (saturating-add (car candidate) 1 (- (length lines) 1)))
+                          (saturating-sub (cadr candidate) 1 0)
+                          (saturating-add (+ (cadr candidate) (caddr candidate)) 1 line-length)))
+        (left (substring (list-ref lines (car candidate))
+                         (saturating-sub (cadr candidate) 1 0)
+                         (cadr candidate)))
+        (right (substring (list-ref lines (car candidate))
+                          (+ (cadr candidate) (caddr candidate))
+                          (saturating-add (+ (cadr candidate) (caddr candidate)) 1 line-length))))
+    (or (contains-part-symbol? above)
+        (contains-part-symbol? below)
+        (contains-part-symbol? left)
+        (contains-part-symbol? right))))
+
+(let* ((port (open-input-file "3.txt"))
+       (lines (read-lines port)))
+  (close-port port)
+  (display (fold + 0 (map cadddr (filter (lambda (cand) (part-number? cand lines)) (find-candidates lines))))))