3 files changed, 62 insertions, 60 deletions
diff --git a/2021/day-06/day-06.livemd b/2021/day-06/day-06.livemd
index 87224e9..5ab794f 100644
--- a/2021/day-06/day-06.livemd
+++ b/2021/day-06/day-06.livemd
@@ -1,3 +1,4 @@
+<!-- vim: set syntax=markdown: -->
 <!-- livebook:{"persist_outputs":true} -->
 
 # Advent of Code 2021, Day 6
diff --git a/2021/day-09/day-09.bak b/2021/day-09/day-09.bak
deleted file mode 100644
index 11ef8e6..0000000
--- a/2021/day-09/day-09.bak
+++ /dev/null
@@ -1,60 +0,0 @@
-#lang racket
-
-(require threading
-         "../jj-aoc.rkt")
-
-(define data
-  (for/vector ([l (in-lines (open-day 9))]
-               #:unless (equal? l ""))
-    (~>> l
-         string->list
-         (map (λ~>> ~a string->number))
-         list->vector)))
-
-(define max-rows (vector-length data))
-(define max-cols (vector-length (vector-ref data 0)))
-(define-values (min-rows min-cols) (values 0 0))
-
-(define (vector2d-ref vec coord)
-  (match-define `(,r ,c) coord)
-  (~> vec
-      (vector-ref r)
-      (vector-ref c)))
-
-(define (adjacent coords)
-  (match-define `(,r ,c) coords)
-  `((,(add1 r) ,c)
-    (,(sub1 r) ,c)
-    (,r ,(add1 c))
-    (,r ,(sub1 c))))
-
-(define (valid-coordinate coord)
-  (match-define `(,r ,c) coord)
-  (and (>= r min-rows)
-       (< r max-rows)
-       (>= c min-cols)
-       (< c max-cols)))
-
-(define (check-adjacent vec coord)
-  (define x (vector2d-ref vec coord))
-  (for*/and ([neighbor (in-list (adjacent coord))]
-             #:when (valid-coordinate neighbor))
-    (x . < . (vector2d-ref vec neighbor))))
-
-;; part 1
-(for*/sum ([r (in-range min-rows max-rows)]
-           [c (in-range min-cols max-cols)]
-           [x (in-value (vector2d-ref data `(,r ,c)))]
-           #:when (check-adjacent data `(,r ,c)))
-  (add1 x))
-
-;; part 2
-(define visited (make-hash))
-(define (flood-fill vec coord)
-  (if (and (< (vector2d-ref vec coord) 9)
-           (not (hash-has-key? visited coord)))
-      ((hash-set! visited coord 'visited)
-       (add1 (for/sum [(neighbor (in-list (adjacent coord)))
-                       #:when (valid-coordinate neighbor)]
-               (flood-fill vec neighbor))))
-      0))
-\ No newline at end of file
diff --git a/2021/day-10/day-10.rkt b/2021/day-10/day-10.rkt
new file mode 100644
index 0000000..d40d1ea
--- /dev/null
+++ b/2021/day-10/day-10.rkt
@@ -0,0 +1,61 @@
+#lang racket
+
+(require math/statistics
+         threading
+         "../../jj-aoc.rkt")
+
+(define chunks
+  (port->lines (open-day 10 2021)))
+
+(define (opening-bracket? c)
+  (member c (string->list "([{<")))
+
+(define (matching-brackets? c-left c-right)
+  (member (string c-left c-right) '("()" "[]" "{}" "<>")))
+
+(define (parse-brackets lst [acc '()])
+  (cond
+    [(empty? lst) acc]
+    [(opening-bracket? (first lst))
+     (parse-brackets (rest lst) (cons (first lst) acc))]
+    [(matching-brackets? (first acc) (first lst))
+     (parse-brackets (rest lst) (rest acc))]
+    [else (get-score (first lst))]))
+
+;; part 1
+(define (get-score c)
+  (match (string c)
+    [")" 3]
+    ["]" 57]
+    ["}" 1197]
+    [">" 25137]))
+
+(define (score-invalid-string chunk)
+  (match (parse-brackets (string->list chunk))
+    [(? list?) 0]
+    [n n]))
+
+(for/sum ([chunk (in-list chunks)]) (score-invalid-string chunk))
+
+;; part 2
+(define (completion-score lst)
+  (for/fold ([score 0])
+            ([c (in-list lst)])
+    (define val
+      (match (string c)
+        ["(" 1]
+        ["[" 2]
+        ["{" 3]
+        ["<" 4]))
+    (+ (* 5 score) val)))
+
+(define (score-incomplete-string chunk)
+  (match (parse-brackets (string->list chunk))
+    [(? list? lst) (completion-score lst)]
+    [n 0]))
+
+(~>> (for*/list ([chunk (in-list chunks)]
+                 [score (in-value (score-incomplete-string chunk))]
+                 #:when (> score 0))
+       score)
+     (median < ))
+\ No newline at end of file