interactive-coding-challenges/bit_manipulation/bit/bit_solution.ipynb

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   "source": [
    "This notebook was prepared by [Donne Martin](https://github.com/donnemartin). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges)."
   ]
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Solution Notebook"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Problem: Implement common bit manipulation operations: get_bit, set_bit, clear_bit, clear_bits_msb_to_index, clear_bits_msb_to_lsb, update_bit.\n",
    "\n",
    "* [Constraints](#Constraints)\n",
    "* [Test Cases](#Test-Cases)\n",
    "* [Algorithm](#Algorithm)\n",
    "* [Code](#Code)\n",
    "* [Unit Test](#Unit-Test)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Constraints\n",
    "\n",
    "* Can we assume the inputs are valid?\n",
    "    * No\n",
    "* Can we assume this fits memory?\n",
    "    * Yes"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Test Cases\n",
    "\n",
    "* None as a number input -> Exception\n",
    "* Negative index -> Exception\n",
    "\n",
    "### get_bit\n",
    "    number   = 0b10001110, index = 3\n",
    "    expected = True\n",
    "### set_bit\n",
    "    number   = 0b10001110, index = 4\n",
    "    expected = 0b10011110\n",
    "### clear_bit\n",
    "    number   = 0b10001110, index = 3\n",
    "    expected = 0b10000110\n",
    "### clear_bits_msb_to_index\n",
    "    number   = 0b10001110, index = 3\n",
    "    expected = 0b00000110\n",
    "### clear_bits_index_to_lsb\n",
    "    number   = 0b10001110, index = 3\n",
    "    expected = 0b10000000\n",
    "### update_bit\n",
    "    number   = 0b10001110, index = 3, value = 1\n",
    "    expected = 0b10001110\n",
    "    number   = 0b10001110, index = 3, value = 0\n",
    "    expected = 0b10000110\n",
    "    number   = 0b10001110, index = 0, value = 1\n",
    "    expected = 0b10001111"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Algorithm\n",
    "\n",
    "### get_bit\n",
    "\n",
    "<pre>\n",
    "indices  7 6 5 4  3 2 1 0  index = 3\n",
    "--------------------------------------------------\n",
    "input    1 0 0 0  1 1 1 0  0b10001110\n",
    "mask     0 0 0 0  1 0 0 0  1 << index\n",
    "--------------------------------------------------\n",
    "result   0 0 0 0  1 0 0 0  number & mask != 0\n",
    "</pre>\n",
    "\n",
    "Complexity:\n",
    "* Time: O(n)\n",
    "* Space: O(n)\n",
    "\n",
    "### set_bit\n",
    "\n",
    "<pre>\n",
    "indices  7 6 5 4  3 2 1 0  index = 4\n",
    "--------------------------------------------------\n",
    "input    1 0 0 0  1 1 1 0  0b10001110\n",
    "mask     0 0 0 1  0 0 0 0  1 << index\n",
    "--------------------------------------------------\n",
    "result   1 0 0 1  1 1 1 0  number | mask\n",
    "</pre>\n",
    "\n",
    "Complexity:\n",
    "* Time: O(n)\n",
    "* Space: O(n)\n",
    "\n",
    "### clear_bit\n",
    "\n",
    "<pre>\n",
    "indices  7 6 5 4  3 2 1 0  index = 3\n",
    "--------------------------------------------------\n",
    "input    1 0 0 0  1 1 1 0  0b10001110\n",
    "mask     0 0 0 0  1 0 0 0  1 << index\n",
    "mask     1 1 1 1  0 1 1 1  ~(1 << index)\n",
    "--------------------------------------------------\n",
    "result   1 0 0 0  0 1 1 0  number & mask\n",
    "</pre>\n",
    "\n",
    "Complexity:\n",
    "* Time: O(n)\n",
    "* Space: O(n)\n",
    "\n",
    "### clear_bits_msb_to_index\n",
    "\n",
    "<pre>\n",
    "indices  7 6 5 4  3 2 1 0  index = 3\n",
    "--------------------------------------------------\n",
    "input    1 0 0 0  1 1 1 0  0b10001110\n",
    "mask     0 0 0 0  1 0 0 0  1 << index\n",
    "mask     0 0 0 0  0 1 1 1  (1 << index) - 1\n",
    "--------------------------------------------------\n",
    "result   0 0 0 0  0 1 1 1  number & mask\n",
    "</pre>\n",
    "\n",
    "Complexity:\n",
    "* Time: O(n)\n",
    "* Space: O(n)\n",
    "\n",
    "### clear_bits_index_to_lsb\n",
    "\n",
    "<pre>\n",
    "indices  7 6 5 4  3 2 1 0  index = 3\n",
    "--------------------------------------------------\n",
    "input    1 0 0 0  1 1 1 0  0b10001110\n",
    "mask     0 0 0 1  0 0 0 0  1 << index + 1\n",
    "mask     0 0 0 0  1 1 1 1  (1 << index + 1) - 1\n",
    "mask     1 1 1 1  0 0 0 0  ~((1 << index + 1) - 1)\n",
    "--------------------------------------------------\n",
    "result   1 0 0 0  0 0 0 0  number & mask\n",
    "</pre>\n",
    "\n",
    "Complexity:\n",
    "* Time: O(n)\n",
    "* Space: O(n)\n",
    "\n",
    "### update_bit\n",
    "\n",
    "* Use `get_bit` to see if the value is already set or cleared\n",
    "* If not, use `set_bit` if setting the value or `clear_bit` if clearing the value\n",
    "\n",
    "Complexity:\n",
    "* Time: O(n)\n",
    "* Space: O(n)\n",
    "\n",
    "\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": true
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   "outputs": [],
   "source": [
    "def validate_index(func):\n",
    "    def validate_index_wrapper(self, *args, **kwargs):\n",
    "        for arg in args:\n",
    "            if arg < 0:\n",
    "                raise IndexError('Invalid index')\n",
    "        return func(self, *args, **kwargs)\n",
    "    return validate_index_wrapper"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
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   "outputs": [],
   "source": [
    "class Bit(object):\n",
    "\n",
    "    def __init__(self, number):\n",
    "        if number is None:\n",
    "            raise TypeError('number cannot be None')\n",
    "        self.number = number\n",
    "\n",
    "    @validate_index\n",
    "    def get_bit(self, index):\n",
    "        mask = 1 << index\n",
    "        return self.number & mask != 0\n",
    "\n",
    "    @validate_index\n",
    "    def set_bit(self, index):\n",
    "        mask = 1 << index\n",
    "        self.number |= mask\n",
    "        return self.number\n",
    "\n",
    "    @validate_index\n",
    "    def clear_bit(self, index):\n",
    "        mask = ~(1 << index)\n",
    "        self.number &= mask\n",
    "        return self.number\n",
    "\n",
    "    @validate_index\n",
    "    def clear_bits_msb_to_index(self, index):\n",
    "        mask = (1 << index) - 1\n",
    "        self.number &= mask\n",
    "        return self.number\n",
    "\n",
    "    @validate_index\n",
    "    def clear_bits_index_to_lsb(self, index):\n",
    "        mask = ~((1 << index + 1) - 1)\n",
    "        self.number &= mask\n",
    "        return self.number\n",
    "\n",
    "    @validate_index\n",
    "    def update_bit(self, index, value):\n",
    "        if value is None or value not in (0, 1):\n",
    "            raise Exception('Invalid value')\n",
    "        if self.get_bit(index) == value:\n",
    "            return self.number\n",
    "        if value:\n",
    "            self.set_bit(index)\n",
    "        else:\n",
    "            self.clear_bit(index)\n",
    "        return self.number"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Unit Test"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Overwriting test_bit.py\n"
     ]
    }
   ],
   "source": [
    "%%writefile test_bit.py\n",
    "from nose.tools import assert_equal\n",
    "\n",
    "\n",
    "class TestBit(object):\n",
    "\n",
    "    def test_bit(self):\n",
    "        number = int('10001110', base=2)\n",
    "        bit = Bit(number)\n",
    "        assert_equal(bit.get_bit(index=3), True)\n",
    "        expected = int('10011110', base=2)\n",
    "        assert_equal(bit.set_bit(index=4), expected)\n",
    "        bit = Bit(number)\n",
    "        expected = int('10000110', base=2)\n",
    "        assert_equal(bit.clear_bit(index=3), expected)\n",
    "        bit = Bit(number)\n",
    "        expected = int('00000110', base=2)\n",
    "        assert_equal(bit.clear_bits_msb_to_index(index=3), expected)\n",
    "        bit = Bit(number)\n",
    "        expected = int('10000000', base=2)\n",
    "        assert_equal(bit.clear_bits_index_to_lsb(index=3), expected)\n",
    "        bit = Bit(number)\n",
    "        assert_equal(bit.update_bit(index=3, value=1), number)\n",
    "        bit = Bit(number)\n",
    "        expected = int('10000110', base=2)\n",
    "        assert_equal(bit.update_bit(index=3, value=0), expected)\n",
    "        bit = Bit(number)\n",
    "        expected = int('10001111', base=2)\n",
    "        assert_equal(bit.update_bit(index=0, value=1), expected)\n",
    "        print('Success: test_bit')\n",
    "\n",
    "\n",
    "def main():\n",
    "    test = TestBit()\n",
    "    test.test_bit()\n",
    "\n",
    "\n",
    "if __name__ == '__main__':\n",
    "    main()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false
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   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Success: test_bit\n"
     ]
    }
   ],
   "source": [
    "%run -i test_bit.py"
   ]
  }
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