From 77518b3a93d795134b7f90ff9287ade6794f32b9 Mon Sep 17 00:00:00 2001
From: Donne Martin <donne.martin@gmail.com>
Date: Tue, 2 Jun 2015 17:45:02 -0400
Subject: [PATCH] Added notebook solving the following: Implement a hash table
 with set, get, and remove methods.

---
 arrays-strings/hash-map.ipynb | 192 ++++++++++++++++++++++++++++++++++
 1 file changed, 192 insertions(+)
 create mode 100644 arrays-strings/hash-map.ipynb

diff --git a/arrays-strings/hash-map.ipynb b/arrays-strings/hash-map.ipynb
new file mode 100644
index 0000000..ccbb702
--- /dev/null
+++ b/arrays-strings/hash-map.ipynb
@@ -0,0 +1,192 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Problem: Implement a hash table with set, get, and remove methods.\n",
+    "\n",
+    "* [Clarifying Questions](#Clarifying-Questions)\n",
+    "* [Test Cases](#Test-Cases)\n",
+    "* [Algorithm](#Algorithm)\n",
+    "* [Code](#Code)\n",
+    "* [Pythonic-Code](#Pythonic-Code)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Clarifying Questions\n",
+    "\n",
+    "* Are the keys integers only?\n",
+    "    * Yes"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "* get on an empty hash table index\n",
+    "* set on an empty hash table index\n",
+    "* set on a non empty hash table index\n",
+    "* set on a key that already exists\n",
+    "* remove on a key with an entry\n",
+    "* remove on a key without an entry"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm\n",
+    "\n",
+    "### Hash Function\n",
+    "\n",
+    "* Return key % table size\n",
+    "\n",
+    "Complexity:\n",
+    "* Time: O(1)\n",
+    "* Space: O(1)\n",
+    "\n",
+    "### Set\n",
+    "\n",
+    "* Get hash index for lookup\n",
+    "* If key exists, replace\n",
+    "* Else, add\n",
+    "\n",
+    "Complexity:\n",
+    "* Time: O(1) average and best, O(n) worst\n",
+    "* Space: O(1) space for newly added element\n",
+    "\n",
+    "### Get\n",
+    "\n",
+    "* Get hash index for lookup\n",
+    "* If key exists, return value\n",
+    "* Else, return NULL\n",
+    "\n",
+    "Complexity:\n",
+    "* Time: O(1) average and best, O(n) worst\n",
+    "* Space: O(1)\n",
+    "\n",
+    "### Remove\n",
+    "\n",
+    "* Get hash index for lookup\n",
+    "* If key exists, delete the item\n",
+    "\n",
+    "Complexity:\n",
+    "* Time: O(1) average and best, O(n) worst\n",
+    "* Space: O(1)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Code"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "class Item(object):\n",
+    "    def __init__(self, key, value):\n",
+    "        self.key = key\n",
+    "        self.value = value\n",
+    "\n",
+    "class HashTable(object):\n",
+    "    def __init__(self, size):\n",
+    "        self.size = size\n",
+    "        self.table = [[] for _ in xrange(self.size)]\n",
+    "\n",
+    "    def hash_function(self, key):\n",
+    "        return key % self.size\n",
+    "\n",
+    "    def set(self, key, value):\n",
+    "        hash_index = self.hash_function(key)\n",
+    "        for item in self.table[hash_index]:\n",
+    "            if item.key == key:\n",
+    "                item.value = value\n",
+    "                return\n",
+    "        self.table[hash_index].append(Item(key, value))\n",
+    "\n",
+    "    def get(self, key):\n",
+    "        hash_index = self.hash_function(key)\n",
+    "        for item in self.table[hash_index]:\n",
+    "            if item.key == key:\n",
+    "                return item.value\n",
+    "        return None\n",
+    "\n",
+    "    def remove(self, key):\n",
+    "        hash_index = self.hash_function(key)\n",
+    "        for i, item in enumerate(self.table[hash_index]):\n",
+    "            if item.key == key:\n",
+    "                del self.table[hash_index][i]"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "#* get and set on an empty hash\n",
+    "#* get and set on a non empty hash\n",
+    "#* get and set on a hash index with collision\n",
+    "table_size = 10\n",
+    "hash_table = HashTable(table_size)\n",
+    "print(\"get on an empty hash table index\")\n",
+    "print(hash_table.get(0))\n",
+    "print(\"set on an empty hash table index\")\n",
+    "hash_table.set(0, 'foo')\n",
+    "print(hash_table.get(0))\n",
+    "hash_table.set(1, 'bar')\n",
+    "print(hash_table.get(1))\n",
+    "print(\"set on a non empty hash table index\")\n",
+    "hash_table.set(10, 'foo2')\n",
+    "print(hash_table.get(0))\n",
+    "print(hash_table.get(10))\n",
+    "print(\"set on a key that already exists\")\n",
+    "hash_table.set(10, 'foo3')\n",
+    "print(hash_table.get(0))\n",
+    "print(hash_table.get(10))\n",
+    "print(\"remove on a key that already exists\")\n",
+    "hash_table.remove(10)\n",
+    "print(hash_table.get(0))\n",
+    "print(hash_table.get(10))\n",
+    "print(\"remove on a key that doesn't exist\")\n",
+    "hash_table.remove(-1)"
+   ]
+  }
+ ],
+ "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": "2.7.9"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}