1 files changed, 55 insertions, 0 deletions
diff --git a/day3.scm b/day3.scm
new file mode 100755
index 0000000..21fadf0
--- /dev/null
+++ b/day3.scm
@@ -0,0 +1,55 @@
+#!/usr/bin/env gosh
+(use file.util)
+(use util.match)
+(use scheme.set)
+(use gauche.sequence)
+
+(define (read-input filename)
+  (let ((parse-entry 
+          (lambda (x)
+            (cons (string-ref x 0) 
+                  (string->number (substring x 1 (string-length x)))))))
+  (map (lambda (x) (map parse-entry x))
+    (map (lambda (x) (string-split x ",")) 
+         (file->string-list filename)))))
+
+(define (get-path steps x y acc)
+  (if (equal? '() steps) 
+    acc
+    (match (car steps)
+      [`(#\U . ,distance) 
+        (get-path (cdr steps) (+ x distance) y (append acc (map (lambda (dx) (cons (+ x dx) y) ) (iota distance 1))))]
+      [`(#\D . ,distance)
+        (get-path (cdr steps) (- x distance) y (append acc (map (lambda (dx) (cons (- x dx) y) ) (iota distance 1))))]
+      [`(#\L . ,distance)
+        (get-path (cdr steps) x (- y distance) (append acc (map (lambda (dy) (cons x (- y dy)) ) (iota distance 1))))]
+      [`(#\R . ,distance)
+        (get-path (cdr steps) x (+ y distance) (append acc (map (lambda (dy) (cons x (+ y dy)) ) (iota distance 1))))])))
+
+(define (intersections steps)
+  (set->list (apply set-intersection
+                (map (lambda (list) (list->set equal-comparator (get-path list 0 0 '())))
+                  steps))))
+
+(define (part1 input)
+  (letrec ((manhattan-distance
+            (lambda (x)
+              (+ (abs (car x)) (abs (cdr x))))))
+    (car (sort (map manhattan-distance (intersections input))))))
+
+(define (part2 input)
+  (letrec ((first-wire 
+            (get-path (car input) 0 0 '()))
+           (second-wire 
+            (get-path (cadr input) 0 0 '()))
+           (linear-distance
+            (lambda (x)
+              (+ (find-index (lambda (y) (equal? x y)) first-wire)
+                 (find-index (lambda (y) (equal? x y)) second-wire)
+                 2))))
+    (car (sort (map linear-distance (intersections input))))))
+
+(define (main args)
+  (let ((input (read-input "inputs/day3.txt")))
+    (print (part1 input))
+    (print (part2 input))))
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