From 2e904e83f6fbc001e5b265d94283841a51050fac Mon Sep 17 00:00:00 2001
From: Juan Marín Noguera <juan@mnpi.eu>
Date: Sun, 15 Dec 2024 11:59:53 +0100
Subject: Days 08--12

These days have been done while traveling, so they may be less modular
due to time/phone-screen constraints.
---
 day11.scm | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 day11.scm

(limited to 'day11.scm')

diff --git a/day11.scm b/day11.scm
new file mode 100644
index 0000000..76ca159
--- /dev/null
+++ b/day11.scm
@@ -0,0 +1,72 @@
+(define-module (day11)
+	       #:use-module (ice-9 rdelim))
+
+(define (part1 port)
+  (define line (read-line port))
+  (define nums (map string->number (string-split line #\space)))
+  (define (blink lst acc)
+    (if (null? lst) 
+      (reverse acc)
+      (blink (cdr lst)
+	     (if (zero? (car lst))
+	       (cons 1 acc)
+	       (let ((s (number->string (car lst))))
+		 (if (even? (string-length s))
+		   (cons (string->number (substring s (/ (string-length s) 2)))
+			 (cons (string->number (substring s 0 (/ (string-length s) 2)))
+			       acc))
+		   (cons (* (car lst) 2024) acc)))))))
+  (define (iter lst left)
+    (if (zero? left)
+      (length lst)
+      (iter (blink lst '()) (- left 1))))
+  (iter nums 25))
+
+(define memo (make-hash-table))
+
+(define (next0 num)
+  (if (zero? num)
+    (list 1)
+    (let* ((s (number->string num))
+	   (len (string-length s)))
+      (if (even? len)
+	(list (string->number (substring s 0 (/ len 2)))
+	      (string->number (substring s (/ len 2))))
+	(list (* num 2024))))))
+
+(define (next num)
+  (define val (hashv-ref memo num))
+  (if val
+    val
+    (let ((comp (next0 num)))
+      (hashv-set! memo num comp)
+      comp)))
+
+(define (step ht)
+  (define new (make-hash-table))
+  (hash-for-each
+    (lambda (num amt)
+      (for-each
+	(lambda (v)
+	  (hashv-set! new v
+		      (+ (hashv-ref new v 0) amt)))
+	(next num)))
+    ht)
+  new)
+
+(define (part2 port)
+  (define line (read-line port))
+  (define nums (map string->number (string-split line #\space)))
+  (define ht (make-hash-table))
+  (for-each (lambda (n)
+	      (hashv-set! ht n
+			 (+ 1 (hashv-ref ht n 0))))
+	    nums)
+  (define (iter ht left)
+    (if (zero? left)
+      (let ((cnt 0))
+	(hash-for-each (lambda (k v) (set! cnt (+ cnt v)))
+		       ht)
+	cnt)
+      (iter (step ht) (- left 1))))
+  (iter ht 75))
-- 
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