Added compress challenge.

arrays_strings/compress/compress_solution.ipynb

@@ -4,7 +4,14 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "<small><i>This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://bit.ly/code-notes).</i></small>"
+    "<small><i>This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://github.com/donnemartin/coding-challenges).</i></small>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Solution Notebook"
    ]
   },
   {
@@ -28,9 +35,9 @@
    "source": [
     "## Constraints\n",
     "\n",
-    "*Problem statements are often intentionally ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
+    "*Problem statements are sometimes ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
     "\n",
-    "* Can I assume the string is ASCII?\n",
+    "* Can we assume the string is ASCII?\n",
     "    * Yes\n",
     "    * Note: Unicode strings could require special handling depending on your language\n",
     "* Can you use additional data structures?  \n",
@@ -47,9 +54,9 @@
    "source": [
     "## Test Cases\n",
     "\n",
-    "* NULL\n",
+    "* None -> None\n",
     "* '' -> ''\n",
-    "* 'ABC' -> 'ABC'\n",
+    "* 'AABBCC' -> 'AABBCC'\n",
     "* 'AAABCCDDDD' -> 'A3B1C2D4'"
    ]
   },
@@ -59,9 +66,7 @@
    "source": [
     "## Algorithm: List\n",
     "\n",
-    "Since Python strings are immutable, we'll use a list of characters instead to exercise in-place string manipulation as you would get with a C string (which is null terminated, as seen in the diagram below).  Python does not use a null-terminator.\n",
-    "\n",
-    "![alt text](https://raw.githubusercontent.com/donnemartin/algorithms-data-structures/master/images/compress_string.jpg)\n",
+    "Since Python strings are immutable, we'll use a list of characters instead to exercise string manipulation as you would get with a C string.  We'll convert the list to a string at the end of the algorithm.\n",
     "\n",
     "* Calculate the size of the compressed string\n",
     "* If the compressed string size is >= string size, return string\n",
@@ -79,7 +84,7 @@
     "\n",
     "Complexity:\n",
     "* Time: O(n)\n",
-    "* Space: O(2m) where m is the size of the compressed list and the resulting string copied from the list"
+    "* Space: O(n) additional space for the list"
    ]
   },
   {
@@ -138,20 +143,15 @@
    "source": [
     "## Algorithm: Byte Array\n",
     "\n",
-    "The byte array algorithm similar when using a list, except we will need to work with the bytearray's character codes instead of the characters as we did above when we implemented this solution with a list.\n",
+    "As a bonus solution, we can solve this problem with a byte array.\n",
+    "\n",
+    "The byte array algorithm similar when using a list, except we will need to work with the bytearray's character codes (using the function ord) instead of the characters as we did above when we implemented this solution with a list.\n",
     "\n",
     "Complexity:\n",
     "* Time: O(n)\n",
     "* Space: O(m) where m is the size of the compressed bytearray"
    ]
   },
-  {
-   "cell_type": "markdown",
-   "metadata": {},
-   "source": [
-    "## Code: Byte Array"
-   ]
-  },
   {
    "cell_type": "code",
    "execution_count": 2,
@@ -201,14 +201,14 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Unit Test"
+    "## Code: Byte Array"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "*It is important to identify and run through general and edge cases from the [Test Cases](#Test-Cases) section by hand.  You generally will not be asked to write a unit test like what is shown below.*"
+    "## Unit Test"
    ]
   },
   {
@@ -217,6 +217,49 @@
    "metadata": {
     "collapsed": false
    },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Overwriting test_compress.py\n"
+     ]
+    }
+   ],
+   "source": [
+    "%%writefile test_compress.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "\n",
+    "class TestCompress(object):\n",
+    "    \n",
+    "    def test_compress(self, func):\n",
+    "        assert_equal(func(None), None)\n",
+    "        assert_equal(func(''), '')\n",
+    "        assert_equal(func('AABBCC'), 'AABBCC')\n",
+    "        assert_equal(func('AAABCCDDDD'), 'A3B1C2D4')\n",
+    "        print('Success: test_compress')\n",
+    "\n",
+    "def main():\n",
+    "    test = TestCompress()\n",
+    "    test.test_compress(compress_string)\n",
+    "    try:\n",
+    "        test.test_compress(compress_string_alt)\n",
+    "    except NameError:\n",
+    "        # Alternate solutions are only defined\n",
+    "        # in the solutions file\n",
+    "        pass\n",
+    "\n",
+    "if __name__ == '__main__':\n",
+    "    main()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {
+    "collapsed": false
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -228,20 +271,7 @@
     }
    ],
    "source": [
-    "from nose.tools import assert_equal\n",
-    "\n",
-    "class Test(object):\n",
-    "    def test_compress(self, func):\n",
-    "        assert_equal(func(None), None)\n",
-    "        assert_equal(func(''), '')\n",
-    "        assert_equal(func('ABC'), 'ABC')\n",
-    "        assert_equal(func('AAABCCDDDD'), 'A3B1C2D4')\n",
-    "        print('Success: test_compress')\n",
-    "\n",
-    "if __name__ == '__main__':\n",
-    "    test = Test()\n",
-    "    test.test_compress(compress_string)\n",
-    "    test.test_compress(compress_string_alt)"
+    "%run -i test_compress.py"
    ]
   }
  ],