{
 "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."
   ]
  }
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