From bc77b0e75f4b4f5f1e4411c9a8e2108875810a60 Mon Sep 17 00:00:00 2001
From: Matthew Butterick <mb@mbtype.com>
Date: Sun, 15 Dec 2019 21:48:17 -0800
Subject: [PATCH] d15 p1

---
 2019/15.rkt  | 24 ++++++++++++++++++++++++
 2019/15.rktd |  1 +
 2 files changed, 25 insertions(+)
 create mode 100644 2019/15.rkt
 create mode 100644 2019/15.rktd

diff --git a/2019/15.rkt b/2019/15.rkt
new file mode 100644
index 0000000..234b73e
--- /dev/null
+++ b/2019/15.rkt
@@ -0,0 +1,24 @@
+#lang br
+(require racket/file rackunit)
+
+(define (make-patintss ints)
+  (for/list ([i (in-range (length ints))])
+    (apply append (map (curry make-list (add1 i)) '(0 1 0 -1)))))
+
+(define (fft str [phase-count 1])
+  (for/fold ([ints (for/list ([c (in-string str)])
+                     (string->number (string c)))]
+             #:result (take ints 8))
+            ([pidx (in-range phase-count)])
+    (for/list ([patints (in-list (make-patintss ints))])
+      (modulo (abs (for/sum ([int (in-list (cons 0 ints))] ; cons 0 to burn off first patint
+                             [patint (in-cycle patints)])
+                     (* int patint))) 10))))
+
+
+(check-equal? (fft "80871224585914546619083218645595" 100) '(2 4 1 7 6 1 7 6))
+(check-equal? (fft "19617804207202209144916044189917" 100) '(7 3 7 4 5 4 1 8))
+(check-equal? (fft "69317163492948606335995924319873" 100) '(5 2 4 3 2 1 3 3))
+
+;; 1
+(check-equal? (fft (file->string "15.rktd") 100) '(8 5 7 2 6 5 0 2))
\ No newline at end of file
diff --git a/2019/15.rktd b/2019/15.rktd
new file mode 100644
index 0000000..19fae88
--- /dev/null
+++ b/2019/15.rktd
@@ -0,0 +1 @@
+59773775883217736423759431065821647306353420453506194937477909478357279250527959717515453593953697526882172199401149893789300695782513381578519607082690498042922082853622468730359031443128253024761190886248093463388723595869794965934425375464188783095560858698959059899665146868388800302242666479679987279787144346712262803568907779621609528347260035619258134850854741360515089631116920328622677237196915348865412336221562817250057035898092525020837239100456855355496177944747496249192354750965666437121797601987523473707071258599440525572142300549600825381432815592726865051526418740875442413571535945830954724825314675166862626566783107780527347044
\ No newline at end of file