1 files changed, 59 insertions, 0 deletions
diff --git a/2021/09/code.tl b/2021/09/code.tl
new file mode 100644
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--- /dev/null
+++ b/2021/09/code.tl
@@ -0,0 +1,59 @@
+(defstruct board ()
+  w h a
+
+  (:method lambda (me x y)
+    (if (or (minusp x)
+            (minusp y)
+            (<= me.w x)
+            (<= me.h y))
+      #\9
+      [[me.a y] x]))
+
+  (:method lambda-set (me x y nv)
+    (set [[me.a y] x] nv)))
+
+(defun read-input (: (name "input"))
+  (flow (file-get-lines name)
+    vec-list
+    (new board
+         h (len @1)
+         w (len (first @1))
+         a @1)))
+
+;;-----------------------------------------------------------------------------
+
+(defun solve-one (bo)
+  (sum-each-prod ((y 0..bo.h)
+                  (x 0..bo.w))
+    (let ((c [bo x y])
+          (u [bo x (pred y)])
+          (d [bo x (succ y)])
+          (l [bo (pred x) y])
+          (r [bo (succ x) y]))
+      (if (and (< c u) (< c d) (< c l) (< c r))
+        (+ 1 (chr-digit c))
+        0))))
+
+;;-----------------------------------------------------------------------------
+
+(defmeth board basin-size (bo x y)
+  (caseq [bo x y]
+    ((#\9 #\space) 0)
+    (t (set [bo x y] #\space)
+       (+ 1
+          bo.(basin-size x (pred y))
+          bo.(basin-size x (succ y))
+          bo.(basin-size (pred x) y)
+          bo.(basin-size (succ x) y)))))
+
+(defun solve-two (bo)
+  (flow
+    (build
+      (each-prod ((y 0..bo.h)
+                  (x 0..bo.w))
+        (let* ((bs bo.(basin-size x y)))
+          (if (plusp bs)
+            (add bs)))))
+    sort
+    (nthlast 3)
+    prod))