Reworked algorithm descriptions. Added notebook index. Minor cleanup.

arrays-strings/unique_chars.ipynb

@@ -4,7 +4,16 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Problem: Implement an algorithm to determine if a string has all unique characters"
+    "## Problem: Implement an algorithm to determine if a string has all unique characters\n",
+    "\n",
+    "* [Clarifying Questions](#Clarifying-Questions)\n",
+    "* [Test Cases](#Test-Cases)\n",
+    "* [Algorithm 1: Sets and Length Comparison](#Algorithm-1:-Sets-and-Length-Comparison)\n",
+    "* [Code: Sets and Length Comparison](#Code:-Sets-and-Length-Comparison)\n",
+    "* [Algorithm 2: Hash Map Lookup](#Algorithm-2:-Hash-Map-Lookup)\n",
+    "* [Code: Hash Map Lookup](#Code:-Hash-Map-Lookup)\n",
+    "* [Algorithm 3: In-Place](#Algorithm-3:-In-Place)\n",
+    "* [Code: In-Place](#Code:-In-Place)"
    ]
   },
   {
@@ -13,7 +22,7 @@
    "source": [
     "## Clarifying Questions\n",
     "* Is the string in ASCII (extended?) or Unicode?  \n",
-    "    * ASCII extended, which is 256 characters.\n",
+    "    * ASCII extended, which is 256 characters\n",
     "* Can you use additional data structures?  \n",
     "    * Yes"
    ]
@@ -24,40 +33,34 @@
    "source": [
     "## Test Cases\n",
     "\n",
-    "* \"\" -> True\n",
+    "* '' -> True\n",
-    "* \"foo\" -> False\n",
+    "* 'foo' -> False\n",
-    "* \"bar\" -> True"
+    "* 'bar' -> True"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Algorithm\n",
+    "## Algorithm 1: Sets and Length Comparison\n",
     "\n",
-    "We'll keep a hash map (set) to keep track of unique characters we encounter.  \n",
+    "A set is an unordered collection of unique elements.  \n",
-    "\n",
-    "Note:\n",
-    "* We could also use a dictionary, but it seems more logical to use a set as it does not contain duplicate elements.\n",
-    "* Since the characters are in ASCII, we could potentially use an array of size 128 (or 256 for extended ASCII)\n",
-    "\n",
-    "Steps:\n",
-    "* Scan each character.\n",
-    "* For each character:\n",
-    "    * If the character does not exist in a hash map, add the character to a hash map.\n",
-    "    * Else, return False.\n",
-    "* Return True\n",
     "\n",
+    "* If the length of the set(string) equals the length of the string\n",
+    "    * Return True\n",
+    "* Else\n",
+    "    * Return False\n",
+    "    \n",
     "Complexity:\n",
-    "* Time: O(n).\n",
+    "* Time: O(n)\n",
-    "* Space: Additional O(m), where m is the number of unique characters in the hash map."
+    "* Space: Additional O(m), where m is the number of unique characters in the set"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Code"
+    "## Code: Sets and Length Comparison"
    ]
   },
   {
@@ -69,13 +72,7 @@
    "outputs": [],
    "source": [
     "def unique_chars(string):\n",
-    "    chars_set = set()\n",
+    "    return len(set(string)) == len(string)\n",
-    "    for char in string:\n",
-    "        if char in chars_set:\n",
-    "            return False\n",
-    "        else:\n",
-    "            chars_set.add(char)\n",
-    "    return True\n",
     "\n",
     "print(unique_chars(''))\n",
     "print(unique_chars('foo'))\n",
@@ -86,10 +83,59 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Algorithm: No Additional Data Structures\n",
+    "## Algorithm 2: Hash Map Lookup\n",
+    "\n",
+    "We'll keep a hash map (set) to keep track of unique characters we encounter.  \n",
+    "\n",
+    "Steps:\n",
+    "* Scan each character\n",
+    "* For each character:\n",
+    "    * If the character does not exist in a hash map, add the character to a hash map\n",
+    "    * Else, return False\n",
+    "* Return True\n",
+    "\n",
+    "Notes:\n",
+    "* We could also use a dictionary, but it seems more logical to use a set as it does not contain duplicate elements\n",
+    "* Since the characters are in ASCII, we could potentially use an array of size 128 (or 256 for extended ASCII)\n",
+    "\n",
+    "Complexity:\n",
+    "* Time: O(n)\n",
+    "* Space: Additional O(m), where m is the number of unique characters in the hash map"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Code: Hash Map Lookup"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "def unique_chars_alt(string):\n",
+    "    chars_set = set()\n",
+    "    for char in string:\n",
+    "        if char in chars_set:\n",
+    "            return False\n",
+    "        else:\n",
+    "            chars_set.add(char)\n",
+    "    return True"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm 3: In-Place\n",
     "\n",
     "Since we cannot use additional data structures, this will eliminate the fast lookup O(1) time provided by our hash map.\n",
-    "* Scan each character.\n",
+    "* Scan each character\n",
     "* For each character:\n",
     "    * Scan all [other] characters in the array\n",
     "        * Exluding the current character from the scan is rather tricky in Python and results in a non-Pythonic solution\n",
@@ -97,15 +143,15 @@
     "* Return True\n",
     "\n",
     "Algorithm Complexity:\n",
-    "* Time: O(n^2).\n",
+    "* Time: O(n^2)\n",
-    "* Space: In-place."
+    "* Space: In-place"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Code"
+    "## Code: In-Place"
    ]
   },
   {
@@ -122,25 +168,6 @@
     "            return False\n",
     "    return True"
    ]
-  },
-  {
-   "cell_type": "markdown",
-   "metadata": {},
-   "source": [
-    "## Pythonic Solution(s)"
-   ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {
-    "collapsed": false
-   },
-   "outputs": [],
-   "source": [
-    "def unique_chars_alt2(string):\n",
-    "    return len(set(string)) == len(string)"
-   ]
   }
  ],
  "metadata": {