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Add flip bit challenge

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Donne Martin 2017-03-30 05:49:29 -04:00
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0
bit_manipulation/flip_bit/__init__.py Normal file
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bit_manipulation/flip_bit/flip_bit_challenge.ipynb Normal file
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{
"cells": [
{
"cell_type": "markdown",
"metadata": {},
"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)."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"# Challenge Notebook"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Problem: Flip one bit from 0 to 1 to maximize the longest sequence of 1s.\n",
"\n",
"* [Constraints](#Constraints)\n",
"* [Test Cases](#Test-Cases)\n",
"* [Algorithm](#Algorithm)\n",
"* [Code](#Code)\n",
"* [Unit Test](#Unit-Test)\n",
"* [Solution Notebook](#Solution-Notebook)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Constraints\n",
"\n",
"* Is the input an int, base 2?\n",
" * Yes\n",
"* Can we assume the input is a 32 bit number?\n",
" * Yes\n",
"* Do we have to validate the length of the input?\n",
" * No\n",
"* Is the output an int?\n",
" * Yes\n",
"* Can we assume the inputs are valid?\n",
" * No\n",
"* Can we assume we are using a positive number since Python doesn't have an >>> operator?\n",
" * Yes\n",
"* Can we assume this fits memory?\n",
" * Yes"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Test Cases\n",
"\n",
"* None -> Exception\n",
"* All 1's -> Count of 1s\n",
"* All 0's -> 1\n",
"* General case\n",
" * 0000 1111 1101 1101 1111 0011 1111 0000 -> 10 (ten)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Algorithm\n",
"\n",
"Refer to the [Solution Notebook](). If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Code"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {
"collapsed": false
},
"outputs": [],
"source": [
"class Bits(object):\n",
"\n",
" def flip_bit(self, num):\n",
" # TODO: Implement me\n",
" pass"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Unit Test"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**The following unit test is expected to fail until you solve the challenge.**"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {
"collapsed": false
},
"outputs": [],
"source": [
"# %load test_flip_bit.py\n",
"from nose.tools import assert_equal, assert_raises\n",
"\n",
"\n",
"class TestBits(object):\n",
"\n",
" def test_flip_bit(self):\n",
" bits = Bits()\n",
" assert_raises(TypeError, bits.flip_bit, None)\n",
" assert_equal(bits.flip_bit(0), 1)\n",
" assert_equal(bits.flip_bit(-1), bits.MAX_BITS)\n",
" num = int('00001111110111011110001111110000', base=2)\n",
" expected = 10\n",
" assert_equal(bits.flip_bit(num), expected)\n",
" num = int('00000100111011101111100011111011', base=2)\n",
" expected = 9\n",
" assert_equal(bits.flip_bit(num), expected)\n",
" num = int('00010011101110111110001111101111', base=2)\n",
" expected = 10\n",
" assert_equal(bits.flip_bit(num), expected)\n",
" print('Success: test_print_binary')\n",
"\n",
"\n",
"def main():\n",
" test = TestBits()\n",
" test.test_flip_bit()\n",
"\n",
"\n",
"if __name__ == '__main__':\n",
" main()"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Solution Notebook\n",
"\n",
"Review the [Solution Notebook]() for a discussion on algorithms and code solutions."
]
}
],
"metadata": {
"kernelspec": {
"display_name": "Python 3",
"language": "python",
"name": "python3"
},
"language_info": {
"codemirror_mode": {
"name": "ipython",
"version": 3
},
"file_extension": ".py",
"mimetype": "text/x-python",
"name": "python",
"nbconvert_exporter": "python",
"pygments_lexer": "ipython3",
"version": "3.5.0"
}
},
"nbformat": 4,
"nbformat_minor": 0
}

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bit_manipulation/flip_bit/flip_bit_solution.ipynb Normal file
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{
"cells": [
{
"cell_type": "markdown",
"metadata": {},
"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)."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"# Solution Notebook"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Problem: Flip one bit from 0 to 1 to maximize the longest sequence of 1s.\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",
"* Is the input an int, base 2?\n",
" * Yes\n",
"* Can we assume the input is a 32 bit number?\n",
" * Yes\n",
"* Do we have to validate the length of the input?\n",
" * No\n",
"* Is the output an int?\n",
" * Yes\n",
"* Can we assume the inputs are valid?\n",
" * No\n",
"* Can we assume we are using a positive number since Python doesn't have an >>> operator?\n",
" * Yes\n",
"* Can we assume this fits memory?\n",
" * Yes"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Test Cases\n",
"\n",
"* None -> Exception\n",
"* All 1's -> Count of 1s\n",
"* All 0's -> 1\n",
"* General case\n",
" * Trailing zeroes\n",
" * 0000 1111 1101 1101 1111 0011 1111 0000 -> 10 (ten)\n",
" * Trailing ones\n",
" * 0000 1001 1101 1101 1111 0001 1111 0111 -> 9"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Algorithm\n",
"\n",
"* seen = []\n",
"* Build a list of sequence counts\n",
" * Look for 0's\n",
" * This will be 0 length if the input has trailing ones\n",
" * Add sequence length to seen\n",
" * Look for 1's\n",
" * Add sequence length to seen\n",
"* Find the largest sequence of ones looking at seen\n",
" * Loop through seen\n",
" * On each iteration of the loop, flip what we are looking for from 0 to 1 and vice versa\n",
" * If seen[i] represents 1's, continue, we only want to process 0's\n",
" * If this is our first iteration:\n",
" * max_result = seen[i+1] + 1 if seen[i] > 0\n",
" * continue\n",
" * If we are looking at leading zeroes (i == len(seen)-1):\n",
" * result = seen[i-1] + 1\n",
" * If we are looking at one zero:\n",
" * result = seen[i+1] + seen[i-1] + 1\n",
" * If we are looking at multiple zeroes:\n",
" * result = max(seen[i+1], seen[i-1]) + 1\n",
" * Update max_result based on result\n",
"\n",
"We should make a note that Python does not have a logical right shift operator built in. We can either use a positive number or implement one for a 32 bit number:\n",
"\n",
" num % 0x100000000 >> n\n",
" \n",
"Complexity:\n",
"* Time: O(b)\n",
"* Space: O(b)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Code"
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {
"collapsed": false
},
"outputs": [],
"source": [
"class Bits(object):\n",
"\n",
" MAX_BITS = 32\n",
" \n",
" def _build_seen_list(self, num):\n",
" seen = []\n",
" looking_for = 0\n",
" count = 0\n",
" for _ in range(self.MAX_BITS):\n",
" if num & 1 != looking_for:\n",
" seen.append(count)\n",
" looking_for = not looking_for\n",
" count = 0\n",
" count += 1\n",
" num >>= 1\n",
" seen.append(count)\n",
" return seen\n",
" \n",
" def flip_bit(self, num):\n",
" if num is None:\n",
" raise TypeError('num cannot be None')\n",
" if num == -1:\n",
" return self.MAX_BITS\n",
" if num == 0:\n",
" return 1\n",
" seen = self._build_seen_list(num)\n",
" max_result = 0\n",
" looking_for = 0\n",
" for index, count in enumerate(seen):\n",
" result = 0\n",
" # Only look for zeroes\n",
" if looking_for == 1:\n",
" looking_for = not looking_for\n",
" continue\n",
" # First iteration, take trailing zeroes\n",
" # or trailing ones into account\n",
" if index == 0:\n",
" if count != 0:\n",
" # Trailing zeroes\n",
" try:\n",
" result = seen[index + 1] + 1\n",
" except IndexError:\n",
" result = 1\n",
" # Last iteration\n",
" elif index == len(seen) - 1:\n",
" result = 1 + seen[index - 1]\n",
" else:\n",
" # One zero\n",
" if count == 1:\n",
" result = seen[index + 1] + seen[index - 1] + 1\n",
" # Multiple zeroes\n",
" else:\n",
" result = max(seen[index + 1], seen[index - 1]) + 1\n",
" if result > max_result:\n",
" max_result = result\n",
" looking_for = not looking_for\n",
" return max_result"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Unit Test"
]
},
{
"cell_type": "code",
"execution_count": 2,
"metadata": {
"collapsed": false
},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Overwriting test_flip_bit.py\n"
]
}
],
"source": [
"%%writefile test_flip_bit.py\n",
"from nose.tools import assert_equal, assert_raises\n",
"\n",
"\n",
"class TestBits(object):\n",
"\n",
" def test_flip_bit(self):\n",
" bits = Bits()\n",
" assert_raises(TypeError, bits.flip_bit, None)\n",
" assert_equal(bits.flip_bit(0), 1)\n",
" assert_equal(bits.flip_bit(-1), bits.MAX_BITS)\n",
" num = int('00001111110111011110001111110000', base=2)\n",
" expected = 10\n",
" assert_equal(bits.flip_bit(num), expected)\n",
" num = int('00000100111011101111100011111011', base=2)\n",
" expected = 9\n",
" assert_equal(bits.flip_bit(num), expected)\n",
" num = int('00010011101110111110001111101111', base=2)\n",
" expected = 10\n",
" assert_equal(bits.flip_bit(num), expected)\n",
" print('Success: test_print_binary')\n",
"\n",
"\n",
"def main():\n",
" test = TestBits()\n",
" test.test_flip_bit()\n",
"\n",
"\n",
"if __name__ == '__main__':\n",
" main()"
]
},
{
"cell_type": "code",
"execution_count": 3,
"metadata": {
"collapsed": false
},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Success: test_print_binary\n"
]
}
],
"source": [
"%run -i test_flip_bit.py"
]
}
],
"metadata": {
"kernelspec": {
"display_name": "Python 3",
"language": "python",
"name": "python3"
},
"language_info": {
"codemirror_mode": {
"name": "ipython",
"version": 3
},
"file_extension": ".py",
"mimetype": "text/x-python",
"name": "python",
"nbconvert_exporter": "python",
"pygments_lexer": "ipython3",
"version": "3.4.3"
}
},
"nbformat": 4,
"nbformat_minor": 0
}

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bit_manipulation/flip_bit/test_flip_bit.py Normal file
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from nose.tools import assert_equal, assert_raises
class TestBits(object):
def test_flip_bit(self):
bits = Bits()
assert_raises(TypeError, bits.flip_bit, None)
assert_equal(bits.flip_bit(0), 1)
assert_equal(bits.flip_bit(-1), bits.MAX_BITS)
num = int('00001111110111011110001111110000', base=2)
expected = 10
assert_equal(bits.flip_bit(num), expected)
num = int('00000100111011101111100011111011', base=2)
expected = 9
assert_equal(bits.flip_bit(num), expected)
num = int('00010011101110111110001111101111', base=2)
expected = 10
assert_equal(bits.flip_bit(num), expected)
print('Success: test_print_binary')
def main():
test = TestBits()
test.test_flip_bit()
if __name__ == '__main__':
main()