Day09.ipynb

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    "data = {}\n",
    "with open(\"Day09.txt\") as file:\n",
    "    for y, line in enumerate(file):\n",
    "        for x, value in enumerate(line.strip()):\n",
    "            data[x, y] = int(value)"
   ]
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     "text": [
      "CPU times: user 5.86 ms, sys: 0 ns, total: 5.86 ms\n",
      "Wall time: 5.86 ms\n"
     ]
    },
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       "564"
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    "%%time\n",
    "lowpoints = {}\n",
    "for (x, y), value in data.items():\n",
    "    for sx, sy in ((-1, 0), (1, 0), (0, -1), (0, 1)):\n",
    "        if data.get((x + sx, y + sy), 10) <= value:\n",
    "            break\n",
    "    else:\n",
    "        lowpoints[x, y] = value\n",
    "sum(lowpoints.values()) + len(lowpoints)"
   ]
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    "def explore_basin(coords, basin=None):\n",
    "    basin = basin or set()\n",
    "    if coords in basin:\n",
    "        return\n",
    "    if data.get(coords, 10) >= 9:\n",
    "        return\n",
    "    basin.add(coords)\n",
    "    x, y = coords\n",
    "    for sx, sy in ((-1, 0), (1, 0), (0, -1), (0, 1)):\n",
    "        explore_basin((x + sx, y + sy), basin)\n",
    "    return basin"
   ]
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    {
     "name": "stdout",
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     "text": [
      "CPU times: user 9.1 ms, sys: 22 µs, total: 9.12 ms\n",
      "Wall time: 8.86 ms\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "1038240"
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     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
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   ],
   "source": [
    "%%time\n",
    "from functools import reduce\n",
    "from operator import mul\n",
    "\n",
    "basins = (len(explore_basin(coords)) for coords in lowpoints)\n",
    "reduce(mul, sorted(basins, reverse=True)[:3])"
   ]
  }
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