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Add longest substring challenge

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Donne Martin 2017-03-28 05:00:23 -04:00
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0
recursion_dynamic/longest_substring/__init__.py Normal file
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177
recursion_dynamic/longest_substring/longest_common_substr_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: Given two strings, find the longest common substring.\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",
"* Can we assume the inputs are valid?\n",
" * No\n",
"* Can we assume the strings are ASCII?\n",
" * Yes\n",
"* Is this case sensitive?\n",
" * Yes\n",
"* Is a substring a contiguous block of chars?\n",
" * Yes\n",
"* Do we expect a string as a result?\n",
" * Yes\n",
"* Can we assume this fits memory?\n",
" * Yes"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Test Cases\n",
"\n",
"* str0 or str1 is None -> Exception\n",
"* str0 or str1 equals 0 -> ''\n",
"* General case\n",
"\n",
"str0 = 'ABCDEFGHIJ'\n",
"str1 = 'FOOBCDBCDE'\n",
"\n",
"result: 'BCDE'"
]
},
{
"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 StringCompare(object):\n",
"\n",
" def longest_common_substr(self, str0, str1):\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_longest_common_substr.py\n",
"from nose.tools import assert_equal, assert_raises\n",
"\n",
"\n",
"class TestLongestCommonSubstr(object):\n",
"\n",
" def test_longest_common_substr(self):\n",
" str_comp = StringCompare()\n",
" assert_raises(TypeError, str_comp.longest_common_substr, None, None)\n",
" assert_equal(str_comp.longest_common_substr('', ''), '')\n",
" str0 = 'ABCDEFGHIJ'\n",
" str1 = 'FOOBCDBCDE'\n",
" expected = 'BCDE'\n",
" assert_equal(str_comp.longest_common_substr(str0, str1), expected)\n",
" print('Success: test_longest_common_substr')\n",
"\n",
"\n",
"def main():\n",
" test = TestLongestCommonSubstr()\n",
" test.test_longest_common_substr()\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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recursion_dynamic/longest_substring/longest_common_substr_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: Given two strings, find the longest common substring.\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 the strings are ASCII?\n",
" * Yes\n",
"* Is this case sensitive?\n",
" * Yes\n",
"* Is a substring a contiguous block of chars?\n",
" * Yes\n",
"* Do we expect a string as a result?\n",
" * Yes\n",
"* Can we assume this fits memory?\n",
" * Yes"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Test Cases\n",
"\n",
"* str0 or str1 is None -> Exception\n",
"* str0 or str1 equals 0 -> ''\n",
"* General case\n",
"\n",
"str0 = 'ABCDEFGHIJ'\n",
"str1 = 'FOOBCDBCDE'\n",
"\n",
"result: 'BCDE'"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Algorithm\n",
"\n",
"We'll use bottom up dynamic programming to build a table. \n",
"\n",
"<pre>\n",
"\n",
"The rows (i) represent str0.\n",
"The columns (j) represent str1.\n",
"\n",
" str1\n",
" -------------------------------------------------\n",
" | | | A | B | C | D | E | F | G | H | I | J |\n",
" -------------------------------------------------\n",
" | | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |\n",
" | F | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 |\n",
" | O | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 |\n",
"s | O | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 |\n",
"t | B | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |\n",
"r | C | 0 | 0 | 1 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 |\n",
"0 | D | 0 | 0 | 1 | 2 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |\n",
" | B | 0 | 0 | 1 | 2 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |\n",
" | C | 0 | 0 | 1 | 2 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |\n",
" | D | 0 | 0 | 1 | 2 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |\n",
" | E | 0 | 0 | 1 | 2 | 3 | 4 | 4 | 4 | 4 | 4 | 4 |\n",
" -------------------------------------------------\n",
"\n",
"if str1[j] != str0[i]:\n",
" T[i][j] = max(\n",
" T[i][j-1],\n",
" T[i-1][j])\n",
"else:\n",
" T[i][j] = T[i-1][j-1] + 1\n",
"</pre>\n",
"\n",
"Complexity:\n",
"* Time: O(m * n), where m is the length of str0 and n is the length of str1\n",
"* Space: O(m * n), where m is the length of str0 and n is the length of str1"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Code"
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {
"collapsed": false
},
"outputs": [],
"source": [
"class StringCompare(object):\n",
"\n",
" def longest_common_substr(self, str0, str1):\n",
" if str0 is None or str1 is None:\n",
" raise TypeError('str input cannot be None')\n",
" # Add one to number of rows and cols for the dp table's\n",
" # first row of 0's and first col of 0's\n",
" num_rows = len(str0) + 1\n",
" num_cols = len(str1) + 1\n",
" T = [[None] * num_cols for _ in range(num_rows)]\n",
" for i in range(num_rows):\n",
" for j in range(num_cols):\n",
" if i == 0 or j == 0:\n",
" T[i][j] = 0\n",
" elif str0[j-1] != str1[i-1]:\n",
" T[i][j] = max(T[i][j-1],\n",
" T[i-1][j])\n",
" else:\n",
" T[i][j] = T[i-1][j-1] + 1\n",
" results = ''\n",
" i = num_rows - 1\n",
" j = num_cols - 1\n",
" # Walk backwards to determine the substring\n",
" while T[i][j]:\n",
" if T[i][j] == T[i][j-1]:\n",
" j -= 1\n",
" elif T[i][j] == T[i-1][j]:\n",
" i -= 1\n",
" elif T[i][j] == T[i-1][j-1] + 1:\n",
" results += str1[i-1]\n",
" i -= 1\n",
" j -= 1\n",
" else:\n",
" raise Exception('Error constructing table')\n",
" # Walking backwards results in a string in reverse order\n",
" return results[::-1] "
]
},
{
"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_longest_common_substr.py\n"
]
}
],
"source": [
"%%writefile test_longest_common_substr.py\n",
"from nose.tools import assert_equal, assert_raises\n",
"\n",
"\n",
"class TestLongestCommonSubstr(object):\n",
"\n",
" def test_longest_common_substr(self):\n",
" str_comp = StringCompare()\n",
" assert_raises(TypeError, str_comp.longest_common_substr, None, None)\n",
" assert_equal(str_comp.longest_common_substr('', ''), '')\n",
" str0 = 'ABCDEFGHIJ'\n",
" str1 = 'FOOBCDBCDE'\n",
" expected = 'BCDE'\n",
" assert_equal(str_comp.longest_common_substr(str0, str1), expected)\n",
" print('Success: test_longest_common_substr')\n",
"\n",
"\n",
"def main():\n",
" test = TestLongestCommonSubstr()\n",
" test.test_longest_common_substr()\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_longest_common_substr\n"
]
}
],
"source": [
"%run -i test_longest_common_substr.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": "3.5.0"
}
},
"nbformat": 4,
"nbformat_minor": 0
}

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recursion_dynamic/longest_substring/test_longest_common_substr.py Normal file
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from nose.tools import assert_equal, assert_raises
class TestLongestCommonSubstr(object):
def test_longest_common_substr(self):
str_comp = StringCompare()
assert_raises(TypeError, str_comp.longest_common_substr, None, None)
assert_equal(str_comp.longest_common_substr('', ''), '')
str0 = 'ABCDEFGHIJ'
str1 = 'FOOBCDBCDE'
expected = 'BCDE'
assert_equal(str_comp.longest_common_substr(str0, str1), expected)
print('Success: test_longest_common_substr')
def main():
test = TestLongestCommonSubstr()
test.test_longest_common_substr()
if __name__ == '__main__':
main()