Added replace char challenge.

arrays_strings/replace_char/replace_char_challenge.ipynb

@@ -0,0 +1,177 @@
+{
+ "cells": [
+  {
+   "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://github.com/donnemartin/coding-challenges).</i></small>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Challenge Notebook"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Problem: Given a string, replace all spaces with '%20', in-place\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",
+    "*Problem statements are sometimes ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
+    "\n",
+    "* Can we 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\n",
+    "* Since Python strings are immutable and we are asked to do this in-place, can I use a bytearray or a list instead?\n",
+    "    * Yes"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "* None -> None\n",
+    "* ' ' -> '%20'\n",
+    "* ' foo bar ' -> '%20foo%20bar%20'\n",
+    "* 'foo' -> 'foo'"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm\n",
+    "\n",
+    "Refer to the [Solution Notebook](http://nbviewer.ipython.org/github/donnemartin/coding-challenges/blob/master/arrays_strings/replace_char/replace_char_solution.ipynb).  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": [
+    "def encode_spaces(string, length):\n",
+    "    # TODO: Implement me\n",
+    "    pass"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Unit Test"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "\n",
+    "\n",
+    "**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_replace_char.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "\n",
+    "class TestReplace(object):\n",
+    "    \n",
+    "    def test_replace_char(self, func):\n",
+    "        # | are used to satisfy the constraint that\n",
+    "        # there is enough space in the string to\n",
+    "        # replace ' ' with '%20'\n",
+    "        # For each space, add two ||\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",
+    "def main():\n",
+    "    test = TestReplace()\n",
+    "    test.test_replace_char(encode_spaces)\n",
+    "    \n",
+    "if __name__ == '__main__':\n",
+    "    main()"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Solution Notebook\n",
+    "\n",
+    "Review the [Solution Notebook](http://nbviewer.ipython.org/github/donnemartin/coding-challenges/blob/master/arrays_strings/replace_char/replace_char_solution.ipynb) for a discussion on algorithms and code solutions."
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 2",
+   "language": "python",
+   "name": "python2"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 2
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython2",
+   "version": "2.7.10"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}

arrays_strings/replace_char/replace_char_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"
    ]
   },
   {
@@ -18,7 +25,8 @@
     "* [Algorithm](#Algorithm)\n",
     "* [Code](#Code)\n",
     "* [Pythonic-Code: Not In-Place](#Pythonic-Code:-Not-In-Place)\n",
-    "* [Unit Test](#Unit-Test)"
+    "* [Unit Test](#Unit-Test)\n",
+    "* [Solution Notebook](#Solution-Notebook)"
    ]
   },
   {
@@ -27,12 +35,14 @@
    "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",
     "* Is there enough space in the data structure for this operation?\n",
+    "    * Yes\n",
+    "* Since Python strings are immutable and we are asked to do this in-place, can I use a bytearray or a list instead?\n",
     "    * Yes"
    ]
   },
@@ -42,7 +52,7 @@
    "source": [
     "## Test Cases\n",
     "\n",
-    "* NULL->NULL\n",
+    "* None -> None\n",
     "* ' ' -> '%20'\n",
     "* ' foo bar ' -> '%20foo%20bar%20'\n",
     "* 'foo' -> 'foo'"
@@ -54,9 +64,7 @@
    "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).  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",
+    "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.\n",
     "\n",
     "* Count the number of spaces in the bytearray\n",
     "* Determine the new bytearray length\n",
@@ -125,6 +133,7 @@
    "source": [
     "import re\n",
     "\n",
+    "\n",
     "def encode_spaces_alt(string):\n",
     "    return re.sub(' ', '%20', string)\n",
     "\n",
@@ -139,13 +148,6 @@
     "## Unit Test"
    ]
   },
-  {
-   "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.*"
-   ]
-  },
   {
    "cell_type": "code",
    "execution_count": 3,
@@ -157,15 +159,21 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "Success: test_replace_char\n"
+      "Overwriting test_replace_char.py\n"
      ]
     }
    ],
    "source": [
+    "%%writefile test_replace_char.py\n",
     "from nose.tools import assert_equal\n",
     "\n",
-    "class Test(object):\n",
+    "\n",
+    "class TestReplace(object):\n",
+    "    \n",
     "    def test_replace_char(self, func):\n",
+    "        # | are used to satisfy the constraint that\n",
+    "        # there is enough space in the string to replace\n",
+    "        # ' ' with '%20'\n",
     "        str0 = None\n",
     "        str1 = bytearray(' ||')\n",
     "        str2 = bytearray(' foo bar ||||||')\n",
@@ -180,9 +188,31 @@
     "        assert_equal(str3, 'foo')\n",
     "        print('Success: test_replace_char')\n",
     "\n",
+    "def main():\n",
+    "    test = TestReplace()\n",
+    "    test.test_replace_char(encode_spaces)\n",
+    "    \n",
     "if __name__ == '__main__':\n",
-    "    test = Test()\n",
-    "    test.test_replace_char(encode_spaces)"
+    "    main()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Success: test_replace_char\n"
+     ]
+    }
+   ],
+   "source": [
+    "run -i test_replace_char.py"
    ]
   }
  ],

arrays_strings/replace_char/test_replace_char.py

@@ -0,0 +1,29 @@
+from nose.tools import assert_equal
+
+
+class TestReplace(object):
+    
+    def test_replace_char(self, func):
+        # | are used to satisfy the constraint that
+        # there is enough space in the string to replace
+        # ' ' with '%20'
+        str0 = None
+        str1 = bytearray(' ||')
+        str2 = bytearray(' foo bar ||||||')
+        str3 = bytearray('foo')
+        func(str0, 0)
+        func(str1, 1)
+        func(str2, 9)
+        func(str3, 3)
+        assert_equal(str0, None)
+        assert_equal(str1, '%20')
+        assert_equal(str2, '%20foo%20bar%20')
+        assert_equal(str3, 'foo')
+        print('Success: test_replace_char')
+
+def main():
+    test = TestReplace()
+    test.test_replace_char(encode_spaces)
+    
+if __name__ == '__main__':
+    main()