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+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "### Advent of Code 2022\n",
+    "#### Day 6: Tuning Trouble\n",
+    "\n",
+    "You're parsing a buffer of characters, looking for a \"marker\": the index of the first character where the previous $n$ characters are all unique.\n",
+    "\n",
+    "**Part 1.** What if $n = 4$, for the \"start of packet\" marker?\n",
+    "\n",
+    "**Part 2.** What if $n = 14$, for the \"start of message\" marker?"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "(require racket\n",
+    "         advent-of-code\n",
+    "         (only-in algorithms sliding))\n"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "##### Parts 1 and 2\n",
+    "\n",
+    "`(sliding xs n)` returns all the overlapping sublists of `xs` that are `n` elements wide.  This turns this problem into a simple `for` comprehension, just looking for the first sublist with no duplicates (which means its length after deduplication doesn't change).\n",
+    "\n",
+    "The solution to part 1 and part 2 is the same, just differing in how wide the window is."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<code>1042</code>"
+      ],
+      "text/plain": [
+       "1042"
+      ]
+     },
+     "execution_count": 2,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "(define buffer (fetch-aoc-input (find-session) 2022 6))\n",
+    "\n",
+    "(define (find-marker data type)\n",
+    "  (define n\n",
+    "    (match type\n",
+    "      ['start-of-packet 4]\n",
+    "      ['start-of-message 14]))\n",
+    "  (for/first ([chunk (in-list (sliding (string->list data) n))]\n",
+    "              [i (in-naturals n)]\n",
+    "              #:when (= n (~> chunk remove-duplicates length)))\n",
+    "    i))\n",
+    "\n",
+    "(find-marker buffer 'start-of-packet)\n",
+    "\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<code>2980</code>"
+      ],
+      "text/plain": [
+       "2980"
+      ]
+     },
+     "execution_count": 3,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "(find-marker buffer 'start-of-message)"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Racket (trusted)",
+   "language": "racket",
+   "name": "racket-trusted"
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+   "codemirror_mode": "scheme",
+   "file_extension": ".rkt",
+   "mimetype": "text/x-racket",
+   "name": "racket",
+   "pygments_lexer": "racket",
+   "version": "8.7"
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