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    "### 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?"
   ]
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   "source": [
    "(require racket\n",
    "         advent-of-code\n",
    "         (only-in algorithms sliding))\n"
   ]
  },
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   "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."
   ]
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    "(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"
   ]
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   "source": [
    "(find-marker buffer 'start-of-message)"
   ]
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