day 05 - eratosthenes sieve.ipynb

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   "source": [
    "import numpy as np"
   ]
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   "source": [
    "## algorithm"
   ]
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   "source": [
    "def eratosthenes(n):\n",
    "    n = (n + 1) >> 1\n",
    "    p = np.ones(n, dtype=np.int8)\n",
    "    i, j = 1, 3\n",
    "    \n",
    "    while i < n:\n",
    "        if p[i]:\n",
    "            p[j * j >> 1::j] = 0\n",
    "        i, j = i + 1, j + 2\n",
    "\n",
    "    return p.sum()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## run"
   ]
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    {
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     "text": [
      "10 4\n",
      "100 25\n",
      "1000 168\n",
      "10000 1229\n",
      "100000 9592\n",
      "1000000 78498\n",
      "10000000 664579\n"
     ]
    }
   ],
   "source": [
    "for j in range(1, 8):\n",
    "    print(10 ** j, eratosthenes(10 ** j))"
   ]
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   "execution_count": null,
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