3 files changed, 81 insertions, 0 deletions
diff --git a/2021/day5/05a.rkt b/2021/day5/05a.rkt
new file mode 100644
index 0000000..c24cb49
--- /dev/null
+++ b/2021/day5/05a.rkt
@@ -0,0 +1,36 @@
+#lang racket
+
+(require "./05a_grammar.rkt")
+
+(define ventCounts (make-hash))
+
+(define (digit x)
+  x)
+
+(define (number . DIGITS)
+  (string->number (foldr string-append "" DIGITS)))
+
+(define (coord a _a b)
+  (list a b))
+
+(define (line c1 _b _c _d _e c2)
+  (define steps (max (abs (- (car c2) (car c1)))
+                     (abs (- (second c2) (second c1)))))
+  (define mx (/ (- (car c2) (car c1)) steps))
+  (define my (/ (- (second c2) (second c1)) steps))
+  (cond [(or (= 0 mx) (= 0 my)) (for ([s (+ 1 steps)])
+                                    (define v (list (+ (car c1) (* mx s)) (+ (second c1) (* my s))))
+                                    (hash-set! ventCounts v (+ 1 (hash-ref ventCounts v 0))))]
+        [else 0]))
+
+
+(define (vents l _a . ls)
+  (cond [(null? ls) l]
+        [else (cons l (apply vents ls))]))
+
+(define-namespace-anchor anc)
+(define ns (namespace-anchor->namespace anc))
+(define parsed (parse-to-datum (file->string "./input")))
+(void (eval parsed ns))
+
+(length (filter (curry <= 2) (hash-values ventCounts)))
diff --git a/2021/day5/05a_grammar.rkt b/2021/day5/05a_grammar.rkt
new file mode 100644
index 0000000..cc78e6a
--- /dev/null
+++ b/2021/day5/05a_grammar.rkt
@@ -0,0 +1,6 @@
+#lang brag
+vents: (line "\n")* ["\n"]
+line: coord " " "-" ">" " " coord
+coord: number "," number
+number: digit*
+digit: "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
diff --git a/2021/day5/05b.rkt b/2021/day5/05b.rkt
new file mode 100644
index 0000000..25d6fd6
--- /dev/null
+++ b/2021/day5/05b.rkt
@@ -0,0 +1,39 @@
+#lang racket
+
+(require "./05a_grammar.rkt")
+
+(define ventCounts (make-hash))
+
+(define (digit x)
+  x)
+
+(define (number . DIGITS)
+  (string->number (foldr string-append "" DIGITS)))
+
+(define (coord a _a b)
+  (list a b))
+
+(define (line c1 _b _c _d _e c2)
+  (define steps (max (abs (- (car c2) (car c1)))
+                     (abs (- (second c2) (second c1)))))
+  (define mx (/ (- (car c2) (car c1)) steps))
+  (define my (/ (- (second c2) (second c1)) steps))
+  (for ([s (+ 1 steps)])
+    (define v (list (+ (car c1) (* mx s)) (+ (second c1) (* my s))))
+    (hash-set! ventCounts v (+ 1 (hash-ref ventCounts v 0)))))
+
+(define (vents l _a . ls)
+  (cond [(null? ls) l]
+        [else (cons l (apply vents ls))]))
+
+(define (print-board ex ey)
+  (for ([y ey])
+    (for ([x ex])
+      (display (hash-ref ventCounts (list x y) ".")))
+    (display "\n")))
+
+(define-namespace-anchor anc)
+(define ns (namespace-anchor->namespace anc))
+(define parsed (parse-to-datum (file->string "./input")))
+(void (eval parsed ns))
+(length (filter (curry <= 2) (hash-values ventCounts)))