day17

2 files changed, 88 insertions, 0 deletions

diff --git a/day17 b/day17
new file mode 100644
index 0000000..9f0e33b
--- /dev/null
+++ b/day17
@@ -0,0 +1 @@
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diff --git a/day17.rkt b/day17.rkt
new file mode 100644
index 0000000..ff07441
--- /dev/null
+++ b/day17.rkt
@@ -0,0 +1,87 @@
+#lang racket
+
+(define pieces
+  '(#(#(#t #t #t #t))
+
+    #(#(#f #t #f)
+      #(#t #t #t)
+      #(#f #t #f))
+
+    #(#(#f #f #t)
+      #(#f #f #t)
+      #(#t #t #t))
+
+    #(#(#t)
+      #(#t)
+      #(#t)
+      #(#t))
+
+    #(#(#t #t)
+      #(#t #t))
+    ))
+
+(define piece-height vector-length)
+(define (piece-width p) (vector-length (vector-ref p 0)))
+
+(define input (list->vector (string->list (car (file->lines "day17")))))
+
+(define stack #())
+
+(define (piece-fit stack piece offset-height offset-width)
+  (for/and ([h (in-range 0 (piece-height piece))])
+    (for/and ([w (in-range 0 (piece-width piece))])
+      (if (and (< -1 (+ offset-height h) (vector-length stack))
+               (< -1 (+ offset-width w) 7))
+        (if (equal? #t (vector-ref (vector-ref piece h) w))
+          (equal? #f (vector-ref (vector-ref stack (+ offset-height h)) (+ offset-width w)))
+          #t)
+        #f))))
+
+(define (piece-place stack piece offset-height offset-width)
+  (for ([h (in-range 0 (piece-height piece))])
+    (for ([w (in-range 0 (piece-width piece))])
+      (when (and (< -1 (+ offset-height h) (vector-length stack))
+                 (< -1 (+ offset-width w) 7)
+                 (equal? #t (vector-ref (vector-ref piece h) w)))
+        (vector-set! (vector-ref stack (+ offset-height h)) (+ offset-width w) #t)))))
+
+(define (drop-piece piece)
+  (set! stack (vector-append (build-vector (+ 3 (piece-height piece))
+                                           (lambda (_)
+                                             (make-vector 7 #f)))
+                             stack))
+
+  (let ([offset-height 0]
+        [offset-width 2])
+    (let loop ()
+      (let ([move (if (equal? (next-move) #\<) -1 1)])
+        (when (piece-fit stack piece offset-height (+ offset-width move))
+          (set! offset-width (+ offset-width move)))
+        (when (piece-fit stack piece (+ 1 offset-height) offset-width)
+          (set! offset-height (+ offset-height 1))
+          (loop))))
+    (piece-place stack piece offset-height offset-width)
+    (let loop2 ([empty-height 0])
+      (if (vector-member #t (vector-ref stack empty-height))
+        (when (> empty-height 0)
+          (set! stack (vector-drop stack empty-height)))
+        (loop2 (+ 1 empty-height)))))
+  )
+
+(define next-move
+  (let ([i 0]
+        [s (vector-length input)])
+    (lambda ()
+      (let ([r (vector-ref input (remainder i s))])
+        (set! i (+ 1 i))
+        r))))
+
+(for ([_ (in-inclusive-range 1 2022)]
+      [piece (in-cycle pieces)])
+  (drop-piece piece))
+
+(vector-length stack)
+;; 3067
+
+; stare at the output
+;; 1514369501484