mirror of
https://github.com/donnemartin/interactive-coding-challenges.git
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Add longest substring challenge
This commit is contained in:
Donne Martin
parent
54cee3457a
commit
391e814d2b
0
recursion_dynamic/longest_substring/__init__.py
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0
recursion_dynamic/longest_substring/__init__.py
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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"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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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# Challenge Notebook"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Problem: Given two strings, find the longest common substring.\n",
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"\n",
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"* [Constraints](#Constraints)\n",
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"* [Test Cases](#Test-Cases)\n",
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"* [Algorithm](#Algorithm)\n",
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"* [Code](#Code)\n",
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"* [Unit Test](#Unit-Test)\n",
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"* [Solution Notebook](#Solution-Notebook)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Constraints\n",
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"\n",
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"* Can we assume the inputs are valid?\n",
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" * No\n",
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"* Can we assume the strings are ASCII?\n",
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" * Yes\n",
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"* Is this case sensitive?\n",
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" * Yes\n",
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"* Is a substring a contiguous block of chars?\n",
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" * Yes\n",
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"* Do we expect a string as a result?\n",
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" * Yes\n",
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"* Can we assume this fits memory?\n",
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" * Yes"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Test Cases\n",
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"\n",
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"* str0 or str1 is None -> Exception\n",
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"* str0 or str1 equals 0 -> ''\n",
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"* General case\n",
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"\n",
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"str0 = 'ABCDEFGHIJ'\n",
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"str1 = 'FOOBCDBCDE'\n",
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"\n",
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"result: 'BCDE'"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Algorithm\n",
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"\n",
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"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."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Code"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {
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"collapsed": false
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},
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"outputs": [],
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"source": [
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"class StringCompare(object):\n",
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"\n",
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" def longest_common_substr(self, str0, str1):\n",
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" # TODO: Implement me\n",
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" pass"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Unit Test"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"**The following unit test is expected to fail until you solve the challenge.**"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {
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"collapsed": false
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},
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"outputs": [],
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"source": [
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"# %load test_longest_common_substr.py\n",
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"from nose.tools import assert_equal, assert_raises\n",
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"\n",
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"\n",
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"class TestLongestCommonSubstr(object):\n",
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"\n",
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" def test_longest_common_substr(self):\n",
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" str_comp = StringCompare()\n",
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" assert_raises(TypeError, str_comp.longest_common_substr, None, None)\n",
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" assert_equal(str_comp.longest_common_substr('', ''), '')\n",
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" str0 = 'ABCDEFGHIJ'\n",
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" str1 = 'FOOBCDBCDE'\n",
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" expected = 'BCDE'\n",
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" assert_equal(str_comp.longest_common_substr(str0, str1), expected)\n",
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" print('Success: test_longest_common_substr')\n",
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"\n",
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"\n",
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"def main():\n",
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" test = TestLongestCommonSubstr()\n",
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" test.test_longest_common_substr()\n",
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"\n",
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"\n",
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"if __name__ == '__main__':\n",
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" main()"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Solution Notebook\n",
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"\n",
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"Review the [Solution Notebook]() for a discussion on algorithms and code solutions."
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]
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 3",
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"language": "python",
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"name": "python3"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.5.0"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 0
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}
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@ -0,0 +1,252 @@
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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"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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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# Solution Notebook"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Problem: Given two strings, find the longest common substring.\n",
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"\n",
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"* [Constraints](#Constraints)\n",
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"* [Test Cases](#Test-Cases)\n",
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"* [Algorithm](#Algorithm)\n",
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"* [Code](#Code)\n",
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"* [Unit Test](#Unit-Test)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Constraints\n",
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"\n",
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"* Can we assume the inputs are valid?\n",
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" * No\n",
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"* Can we assume the strings are ASCII?\n",
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" * Yes\n",
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"* Is this case sensitive?\n",
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" * Yes\n",
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"* Is a substring a contiguous block of chars?\n",
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" * Yes\n",
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"* Do we expect a string as a result?\n",
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" * Yes\n",
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"* Can we assume this fits memory?\n",
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" * Yes"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Test Cases\n",
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"\n",
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"* str0 or str1 is None -> Exception\n",
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"* str0 or str1 equals 0 -> ''\n",
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"* General case\n",
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"\n",
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"str0 = 'ABCDEFGHIJ'\n",
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"str1 = 'FOOBCDBCDE'\n",
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"\n",
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"result: 'BCDE'"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Algorithm\n",
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"\n",
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"We'll use bottom up dynamic programming to build a table. \n",
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"\n",
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"<pre>\n",
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"\n",
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"The rows (i) represent str0.\n",
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"The columns (j) represent str1.\n",
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"\n",
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" str1\n",
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" -------------------------------------------------\n",
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" | | | A | B | C | D | E | F | G | H | I | J |\n",
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" -------------------------------------------------\n",
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" | | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |\n",
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" | F | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 |\n",
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" | O | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 |\n",
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"s | O | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 |\n",
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"t | B | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |\n",
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"r | C | 0 | 0 | 1 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 |\n",
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"0 | D | 0 | 0 | 1 | 2 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |\n",
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" | B | 0 | 0 | 1 | 2 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |\n",
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" | C | 0 | 0 | 1 | 2 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |\n",
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" | D | 0 | 0 | 1 | 2 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |\n",
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" | E | 0 | 0 | 1 | 2 | 3 | 4 | 4 | 4 | 4 | 4 | 4 |\n",
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" -------------------------------------------------\n",
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"\n",
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"if str1[j] != str0[i]:\n",
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" T[i][j] = max(\n",
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" T[i][j-1],\n",
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" T[i-1][j])\n",
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"else:\n",
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" T[i][j] = T[i-1][j-1] + 1\n",
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"</pre>\n",
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"\n",
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"Complexity:\n",
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"* Time: O(m * n), where m is the length of str0 and n is the length of str1\n",
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"* Space: O(m * n), where m is the length of str0 and n is the length of str1"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Code"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 1,
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"metadata": {
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"collapsed": false
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},
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"outputs": [],
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"source": [
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"class StringCompare(object):\n",
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"\n",
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" def longest_common_substr(self, str0, str1):\n",
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" if str0 is None or str1 is None:\n",
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" raise TypeError('str input cannot be None')\n",
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" # Add one to number of rows and cols for the dp table's\n",
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" # first row of 0's and first col of 0's\n",
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" num_rows = len(str0) + 1\n",
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" num_cols = len(str1) + 1\n",
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" T = [[None] * num_cols for _ in range(num_rows)]\n",
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" for i in range(num_rows):\n",
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" for j in range(num_cols):\n",
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" if i == 0 or j == 0:\n",
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" T[i][j] = 0\n",
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" elif str0[j-1] != str1[i-1]:\n",
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" T[i][j] = max(T[i][j-1],\n",
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" T[i-1][j])\n",
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" else:\n",
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" T[i][j] = T[i-1][j-1] + 1\n",
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" results = ''\n",
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" i = num_rows - 1\n",
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" j = num_cols - 1\n",
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" # Walk backwards to determine the substring\n",
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" while T[i][j]:\n",
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" if T[i][j] == T[i][j-1]:\n",
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" j -= 1\n",
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" elif T[i][j] == T[i-1][j]:\n",
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" i -= 1\n",
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" elif T[i][j] == T[i-1][j-1] + 1:\n",
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" results += str1[i-1]\n",
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" i -= 1\n",
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" j -= 1\n",
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" else:\n",
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" raise Exception('Error constructing table')\n",
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" # Walking backwards results in a string in reverse order\n",
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" return results[::-1] "
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Unit Test"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 2,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Overwriting test_longest_common_substr.py\n"
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]
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}
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],
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"source": [
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"%%writefile test_longest_common_substr.py\n",
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"from nose.tools import assert_equal, assert_raises\n",
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"\n",
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"\n",
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"class TestLongestCommonSubstr(object):\n",
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"\n",
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" def test_longest_common_substr(self):\n",
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" str_comp = StringCompare()\n",
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" assert_raises(TypeError, str_comp.longest_common_substr, None, None)\n",
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" assert_equal(str_comp.longest_common_substr('', ''), '')\n",
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" str0 = 'ABCDEFGHIJ'\n",
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" str1 = 'FOOBCDBCDE'\n",
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" expected = 'BCDE'\n",
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" assert_equal(str_comp.longest_common_substr(str0, str1), expected)\n",
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" print('Success: test_longest_common_substr')\n",
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"\n",
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"\n",
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"def main():\n",
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" test = TestLongestCommonSubstr()\n",
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" test.test_longest_common_substr()\n",
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"\n",
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"\n",
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"if __name__ == '__main__':\n",
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" main()"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 3,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Success: test_longest_common_substr\n"
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]
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}
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],
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"source": [
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"%run -i test_longest_common_substr.py"
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]
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 3",
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"language": "python",
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"name": "python3"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.5.0"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 0
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}
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@ -0,0 +1,23 @@
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from nose.tools import assert_equal, assert_raises
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class TestLongestCommonSubstr(object):
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def test_longest_common_substr(self):
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str_comp = StringCompare()
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assert_raises(TypeError, str_comp.longest_common_substr, None, None)
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assert_equal(str_comp.longest_common_substr('', ''), '')
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str0 = 'ABCDEFGHIJ'
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str1 = 'FOOBCDBCDE'
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expected = 'BCDE'
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assert_equal(str_comp.longest_common_substr(str0, str1), expected)
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print('Success: test_longest_common_substr')
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def main():
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test = TestLongestCommonSubstr()
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test.test_longest_common_substr()
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if __name__ == '__main__':
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main()
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