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Added notebook solving the following: Implement a hash table with set, get, and remove methods.
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Donne Martin
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356d212a44
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192
arrays-strings/hash-map.ipynb
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192
arrays-strings/hash-map.ipynb
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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Problem: Implement a hash table with set, get, and remove methods.\n",
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"\n",
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"* [Clarifying Questions](#Clarifying-Questions)\n",
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"* [Test Cases](#Test-Cases)\n",
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"* [Algorithm](#Algorithm)\n",
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"* [Code](#Code)\n",
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"* [Pythonic-Code](#Pythonic-Code)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Clarifying Questions\n",
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"\n",
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"* Are the keys integers only?\n",
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" * Yes"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Test Cases\n",
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"\n",
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"* get on an empty hash table index\n",
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"* set on an empty hash table index\n",
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"* set on a non empty hash table index\n",
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"* set on a key that already exists\n",
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"* remove on a key with an entry\n",
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"* remove on a key without an entry"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Algorithm\n",
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"\n",
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"### Hash Function\n",
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"\n",
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"* Return key % table size\n",
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"\n",
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"Complexity:\n",
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"* Time: O(1)\n",
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"* Space: O(1)\n",
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"\n",
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"### Set\n",
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"\n",
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"* Get hash index for lookup\n",
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"* If key exists, replace\n",
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"* Else, add\n",
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"\n",
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"Complexity:\n",
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"* Time: O(1) average and best, O(n) worst\n",
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"* Space: O(1) space for newly added element\n",
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"\n",
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"### Get\n",
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"\n",
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"* Get hash index for lookup\n",
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"* If key exists, return value\n",
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"* Else, return NULL\n",
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"\n",
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"Complexity:\n",
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"* Time: O(1) average and best, O(n) worst\n",
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"* Space: O(1)\n",
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"\n",
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"### Remove\n",
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"\n",
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"* Get hash index for lookup\n",
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"* If key exists, delete the item\n",
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"\n",
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"Complexity:\n",
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"* Time: O(1) average and best, O(n) worst\n",
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"* Space: O(1)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Code"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"class Item(object):\n",
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" def __init__(self, key, value):\n",
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" self.key = key\n",
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" self.value = value\n",
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"\n",
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"class HashTable(object):\n",
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" def __init__(self, size):\n",
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" self.size = size\n",
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" self.table = [[] for _ in xrange(self.size)]\n",
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"\n",
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" def hash_function(self, key):\n",
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" return key % self.size\n",
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"\n",
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" def set(self, key, value):\n",
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" hash_index = self.hash_function(key)\n",
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" for item in self.table[hash_index]:\n",
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" if item.key == key:\n",
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" item.value = value\n",
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" return\n",
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" self.table[hash_index].append(Item(key, value))\n",
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"\n",
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" def get(self, key):\n",
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" hash_index = self.hash_function(key)\n",
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" for item in self.table[hash_index]:\n",
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" if item.key == key:\n",
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" return item.value\n",
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" return None\n",
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"\n",
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" def remove(self, key):\n",
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" hash_index = self.hash_function(key)\n",
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" for i, item in enumerate(self.table[hash_index]):\n",
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" if item.key == key:\n",
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" del self.table[hash_index][i]"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {
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"collapsed": false
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},
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"outputs": [],
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"source": [
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"#* get and set on an empty hash\n",
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"#* get and set on a non empty hash\n",
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"#* get and set on a hash index with collision\n",
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"table_size = 10\n",
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"hash_table = HashTable(table_size)\n",
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"print(\"get on an empty hash table index\")\n",
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"print(hash_table.get(0))\n",
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"print(\"set on an empty hash table index\")\n",
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"hash_table.set(0, 'foo')\n",
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"print(hash_table.get(0))\n",
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"hash_table.set(1, 'bar')\n",
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"print(hash_table.get(1))\n",
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"print(\"set on a non empty hash table index\")\n",
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"hash_table.set(10, 'foo2')\n",
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"print(hash_table.get(0))\n",
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"print(hash_table.get(10))\n",
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"print(\"set on a key that already exists\")\n",
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"hash_table.set(10, 'foo3')\n",
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"print(hash_table.get(0))\n",
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"print(hash_table.get(10))\n",
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"print(\"remove on a key that already exists\")\n",
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"hash_table.remove(10)\n",
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"print(hash_table.get(0))\n",
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"print(hash_table.get(10))\n",
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"print(\"remove on a key that doesn't exist\")\n",
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"hash_table.remove(-1)"
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]
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 2",
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"language": "python",
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"name": "python2"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 2
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython2",
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"version": "2.7.9"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 0
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}
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