day 06 - postfix notation.ipynb

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    "## algorithm"
   ]
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    "ops = {\n",
    "    '+': float.__add__,\n",
    "    '-': float.__sub__,\n",
    "    '*': float.__mul__,\n",
    "    '/': float.__truediv__,\n",
    "    '^': float.__pow__,\n",
    "}\n",
    "\n",
    "def postfix(expression):\n",
    "    stack = []\n",
    "    \n",
    "    for x in expression.split():\n",
    "        if x in ops:\n",
    "            x = ops[x](stack.pop(-2), stack.pop(-1))\n",
    "        else:\n",
    "            x = float(x)\n",
    "        stack.append(x)\n",
    "        \n",
    "    return stack.pop()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## run"
   ]
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   "cell_type": "code",
   "execution_count": 2,
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   "outputs": [
    {
     "data": {
      "text/plain": [
       "8.0"
      ]
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     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
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   "source": [
    "postfix('1 2 + 4 3 - + 10 5 / *')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
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   "outputs": [
    {
     "data": {
      "text/plain": [
       "25.0"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
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   ],
   "source": [
    "postfix('1 2 * 6 2 / + 9 7 - ^')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "15.0"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
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   "source": [
    "postfix('1 2 3 4 5 + + + +')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
  }
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