From 6cea5d003ab527cd9a3837706476d218684757bd Mon Sep 17 00:00:00 2001
From: Donne Martin <donne.martin@gmail.com>
Date: Wed, 24 Jun 2015 18:23:27 -0400
Subject: [PATCH] Reworked notebook: Added more detail to clarifying questions
 and test cases.  Reworked algorithm discussion, code, and unit test.

---
 arrays-strings/replace_char.ipynb | 102 ++++++++++++++++++------------
 1 file changed, 61 insertions(+), 41 deletions(-)

diff --git a/arrays-strings/replace_char.ipynb b/arrays-strings/replace_char.ipynb
index 4bfb436..2ed6818 100644
--- a/arrays-strings/replace_char.ipynb
+++ b/arrays-strings/replace_char.ipynb
@@ -17,7 +17,8 @@
     "* [Test Cases](#Test-Cases)\n",
     "* [Algorithm](#Algorithm)\n",
     "* [Code](#Code)\n",
-    "* [Pythonic-Code: Not In-Place](#Pythonic-Code:-Not-In-Place)"
+    "* [Pythonic-Code: Not In-Place](#Pythonic-Code:-Not-In-Place)\n",
+    "* [Unit Test](#Unit-Test)"
    ]
   },
   {
@@ -26,8 +27,11 @@
    "source": [
     "## Clarifying Questions\n",
     "\n",
-    "* Is the string ASCII (extended)?  Or Unicode?\n",
-    "    * ASCII extended, which is 256 characters\n",
+    "*Problem statements are sometimes intentionally ambiguous.  Asking clarifying questions, identifying constraints, and stating assumptions help to ensure you code the intended solution.*\n",
+    "\n",
+    "* Can I assume the string is ASCII?\n",
+    "    * Yes\n",
+    "    * Note: Unicode strings could require special handling depending on your language\n",
     "* Is there enough space in the data structure for this operation?\n",
     "    * Yes"
    ]
@@ -38,49 +42,21 @@
    "source": [
     "## Test Cases\n",
     "\n",
+    "*Identifying and running through general and edge cases are important.  You generally will not be asked to write a unit test like what is shown below.*\n",
+    "\n",
     "* NULL->NULL\n",
     "* ' ' -> '%20'\n",
     "* ' foo bar ' -> '%20foo%20bar%20'\n",
     "* 'foo' -> 'foo'"
    ]
   },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {
-    "collapsed": true
-   },
-   "outputs": [],
-   "source": [
-    "from nose.tools import assert_equal\n",
-    "\n",
-    "class Test(object):\n",
-    "    def test_replace_char(self, func):\n",
-    "        str0 = None\n",
-    "        str1 = bytearray(' ||')\n",
-    "        str2 = bytearray(' foo bar ||||||')\n",
-    "        str3 = bytearray('foo')\n",
-    "        func(str0, 0)\n",
-    "        func(str1, 1)\n",
-    "        func(str2, 9)\n",
-    "        func(str3, 3)\n",
-    "        assert_equal(str0, None)\n",
-    "        assert_equal(str1, '%20')\n",
-    "        assert_equal(str2, '%20foo%20bar%20')\n",
-    "        assert_equal(str3, 'foo')\n",
-    "\n",
-    "def run_tests(func):\n",
-    "    test = Test()\n",
-    "    test.test_replace_char(func)"
-   ]
-  },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
     "## Algorithm\n",
     "\n",
-    "Since Python strings are immutable, we'll use a bytearray 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).  For the python bytearray we will not use a null terminator.\n",
+    "Since Python strings are immutable, we'll use a bytearray 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/replace_string.jpg)\n",
     "\n",
@@ -110,7 +86,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 1,
    "metadata": {
     "collapsed": false
    },
@@ -124,14 +100,12 @@
     "    for i in xrange(length-1, -1, -1):\n",
     "        if chr(string[i]) == ' ':\n",
     "            string[new_length] = '0'\n",
-    "            string[new_length - 1] = '2'\n",
-    "            string[new_length - 2] = '%'\n",
+    "            string[new_length-1] = '2'\n",
+    "            string[new_length-2] = '%'\n",
     "            new_length -= 3\n",
     "        else:\n",
     "            string[new_length] = string[i]\n",
-    "            new_length -= 1\n",
-    "\n",
-    "run_tests(encode_spaces)"
+    "            new_length -= 1"
    ]
   },
   {
@@ -145,7 +119,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 2,
    "metadata": {
     "collapsed": false
    },
@@ -159,6 +133,52 @@
     "def encode_spaces_alt2(string):\n",
     "    return string.replace(' ', '%20')"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Unit Test"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Success: test_replace_char\n"
+     ]
+    }
+   ],
+   "source": [
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "class Test(object):\n",
+    "    def test_replace_char(self, func):\n",
+    "        str0 = None\n",
+    "        str1 = bytearray(' ||')\n",
+    "        str2 = bytearray(' foo bar ||||||')\n",
+    "        str3 = bytearray('foo')\n",
+    "        func(str0, 0)\n",
+    "        func(str1, 1)\n",
+    "        func(str2, 9)\n",
+    "        func(str3, 3)\n",
+    "        assert_equal(str0, None)\n",
+    "        assert_equal(str1, '%20')\n",
+    "        assert_equal(str2, '%20foo%20bar%20')\n",
+    "        assert_equal(str3, 'foo')\n",
+    "        print('Success: test_replace_char')\n",
+    "\n",
+    "if __name__ == '__main__':\n",
+    "    test = Test()\n",
+    "    test.test_replace_char(encode_spaces)"
+   ]
   }
  ],
  "metadata": {