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 +}