Function_and_code_reuse.ipynb

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      "please enter an integer: 10\n",
      "3628800\n"
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   "source": [
    "# recusion\n",
    "def fact(n):\n",
    "    if n == 0:\n",
    "        return 1\n",
    "    else:\n",
    "        return n*fact(n-1)\n",
    "num = eval(input(\"please enter an integer: \"))\n",
    "print(fact(abs(int(num))))"
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    "**Tower of Hanoi**<br>\n",
    "write a code to describe the movement<br>\n",
    "input the number of layers and output the whole movement<p>\n",
    "_three pillar A B C, move all the layer from A to C_"
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      "1:A-->C\n",
      "2:A-->B\n",
      "1:C-->B\n",
      "3:A-->C\n",
      "1:B-->A\n",
      "2:B-->C\n",
      "1:A-->C\n",
      "7\n"
     ]
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   "source": [
    "count = 0\n",
    "\n",
    "def hanoi(n, a, b, c):\n",
    "    global count\n",
    "    if n == 1:\n",
    "        print(\"{}:{}-->{}\".format(1, a, c))\n",
    "        count += 1\n",
    "    else:\n",
    "        hanoi(n-1, a, c, b)\n",
    "        print(\"{}:{}-->{}\".format(n, a, c))\n",
    "        hanoi(n-1, b, a, c)\n",
    "        count += 1\n",
    "hanoi(3,'A','B','C')\n",
    "print(count)"
   ]
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    "##### here we use the thought of recusion<br>\n",
    "we view _first (n-1) layer_ as a group<br>\n",
    "our basic goal is to move _group(n-1)_ to B<br>\n",
    "then move _layer n_ to C<br>\n",
    "finally move _group(n-1)_ from B to C"
   ]
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