Add str diff challenge

arrays_strings/str_diff/str_diff_challenge.ipynb

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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: Find the single different char between two strings.\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 strings are ASCII?\n",
+    "    * Yes\n",
+    "* Is case important?\n",
+    "    * The strings are lower case\n",
+    "* Can we assume the inputs are valid?\n",
+    "    * No, check for None\n",
+    "* Can we assume this fits memory?\n",
+    "    * Yes"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "* None input -> TypeError\n",
+    "* 'abcd', 'abcde' -> 'e'\n",
+    "* 'aaabbcdd', 'abdbacade' -> 'e'"
+   ]
+  },
+  {
+   "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 Solution(object):\n",
+    "\n",
+    "    def find_diff(self, s, t):\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_str_diff.py\n",
+    "from nose.tools import assert_equal, assert_raises\n",
+    "\n",
+    "\n",
+    "class TestFindDiff(object):\n",
+    "\n",
+    "    def test_find_diff(self):\n",
+    "        solution = Solution()\n",
+    "        assert_raises(TypeError, solution.find_diff, None)\n",
+    "        assert_equal(solution.find_diff('abcd', 'abcde'), 'e')\n",
+    "        assert_equal(solution.find_diff('aaabbcdd', 'abdbacade'), 'e')\n",
+    "        print('Success: test_find_diff')\n",
+    "\n",
+    "\n",
+    "def main():\n",
+    "    test = TestFindDiff()\n",
+    "    test.test_find_diff()\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
+}

arrays_strings/str_diff/str_diff_solution.ipynb

@@ -0,0 +1,215 @@
+{
+ "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: Find the single different char between two strings.\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 strings are ASCII?\n",
+    "    * Yes\n",
+    "* Is case important?\n",
+    "    * The strings are lower case\n",
+    "* Can we assume the inputs are valid?\n",
+    "    * No, check for None\n",
+    "* Can we assume this fits memory?\n",
+    "    * Yes"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "* None input -> TypeError\n",
+    "* 'abcd', 'abcde' -> 'e'\n",
+    "* 'aaabbcdd', 'abdbacade' -> 'e'"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm\n",
+    "\n",
+    "### Dictionary\n",
+    "\n",
+    "* Keep a dictionary of seen values in s\n",
+    "* Loop through t, decrementing the seen values\n",
+    "    * If the char is not there or if the decrement results in a negative value, return the char\n",
+    "\n",
+    "Complexity:\n",
+    "* Time: O(m+n), where m and n are the lengths of s, t\n",
+    "* Space: O(h), for the dict, where h is the unique chars in s\n",
+    "\n",
+    "### XOR\n",
+    "\n",
+    "* XOR the two strings, which will isolate the differing char\n",
+    "\n",
+    "Complexity:\n",
+    "* Time: O(m+n), where m and n are the lengths of s, t\n",
+    "* Space: O(1), for the dict, where h is the unique chars in s"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Code"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "class Solution(object):\n",
+    "\n",
+    "    def find_diff(self, str1, str2):\n",
+    "        if str1 is None or str2 is None:\n",
+    "            raise TypeError('str1 or str2 cannot be None')\n",
+    "        seen = {}\n",
+    "        for char in str1:\n",
+    "            if char in seen:\n",
+    "                seen[char] += 1\n",
+    "            else:\n",
+    "                seen[char] = 1\n",
+    "        for char in str2:\n",
+    "            try:\n",
+    "                seen[char] -= 1\n",
+    "            except KeyError:\n",
+    "                return char\n",
+    "            if seen[char] < 0:\n",
+    "                return char\n",
+    "        return None\n",
+    "\n",
+    "    def find_diff_xor(self, str1, str2):\n",
+    "        if str1 is None or str2 is None:\n",
+    "            raise TypeError('str1 or str2 cannot be None')\n",
+    "        result = 0\n",
+    "        for char in str1:\n",
+    "            result ^= ord(char)\n",
+    "        for char in str2:\n",
+    "            result ^= ord(char)\n",
+    "        return chr(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_str_diff.py\n"
+     ]
+    }
+   ],
+   "source": [
+    "%%writefile test_str_diff.py\n",
+    "from nose.tools import assert_equal, assert_raises\n",
+    "\n",
+    "\n",
+    "class TestFindDiff(object):\n",
+    "\n",
+    "    def test_find_diff(self):\n",
+    "        solution = Solution()\n",
+    "        assert_raises(TypeError, solution.find_diff, None)\n",
+    "        assert_equal(solution.find_diff('abcd', 'abcde'), 'e')\n",
+    "        assert_equal(solution.find_diff('aaabbcdd', 'abdbacade'), 'e')\n",
+    "        print('Success: test_find_diff')\n",
+    "\n",
+    "\n",
+    "def main():\n",
+    "    test = TestFindDiff()\n",
+    "    test.test_find_diff()\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_find_diff\n"
+     ]
+    }
+   ],
+   "source": [
+    "%run -i test_str_diff.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
+}

arrays_strings/str_diff/test_str_diff.py

@@ -0,0 +1,20 @@
+from nose.tools import assert_equal, assert_raises
+
+
+class TestFindDiff(object):
+
+    def test_find_diff(self):
+        solution = Solution()
+        assert_raises(TypeError, solution.find_diff, None)
+        assert_equal(solution.find_diff('abcd', 'abcde'), 'e')
+        assert_equal(solution.find_diff('aaabbcdd', 'abdbacade'), 'e')
+        print('Success: test_find_diff')
+
+
+def main():
+    test = TestFindDiff()
+    test.test_find_diff()
+
+
+if __name__ == '__main__':
+    main()