2020-11-26_reverse-bits.ipynb

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  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This problem was asked by Facebook.\n",
    "\n",
    "Given a 32-bit integer, return the number with its bits reversed.\n",
    "\n",
    "For example, given the binary number `1111 0000 1111 0000 1111 0000 1111 0000`, return `0000 1111 0000 1111 0000 1111 0000 1111`."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 46,
   "metadata": {},
   "outputs": [],
   "source": [
    "from operator import xor\n",
    "from math import log2\n",
    "\n",
    "def bit_reverse(integer, verbose=True):\n",
    "    \"\"\"Reverse a 32-bit integer.\"\"\"\n",
    "    if integer == 0:\n",
    "        rev = 1\n",
    "    else:\n",
    "        ones = 2 ** int(log2(integer) + 1) - 1\n",
    "        rev = xor(integer, ones)\n",
    "    if verbose:\n",
    "        print(\"reverse of\", bin(integer), \"is\", bin(rev))\n",
    "    return rev"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 47,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "reverse of 0b100000 is 0b11111\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "31"
      ]
     },
     "execution_count": 47,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "bit_reverse(32)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 48,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "reverse of 0b0 is 0b1\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "1"
      ]
     },
     "execution_count": 48,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "bit_reverse(0)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 49,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "reverse of 0b1 is 0b0\n"
     ]
    },
    {
     "data": {
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       "0"
      ]
     },
     "execution_count": 49,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "bit_reverse(1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 50,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "reverse of 0b10 is 0b1\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "1"
      ]
     },
     "execution_count": 50,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "bit_reverse(2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 51,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "reverse of 0b11 is 0b0\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "0"
      ]
     },
     "execution_count": 51,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "bit_reverse(3)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 52,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "reverse of 0b100 is 0b11\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "3"
      ]
     },
     "execution_count": 52,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "bit_reverse(4)"
   ]
  }
 ],
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