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 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This notebook was prepared by [Donne Martin](https://github.com/donnemartin). Source and license info is on [GitHub](https://github.com/donnemartin/system-design-primer)."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Design a hash map"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Constraints and assumptions\n",
    "\n",
    "* For simplicity, are the keys integers only?\n",
    "    * Yes\n",
    "* For collision resolution, can we use chaining?\n",
    "    * Yes\n",
    "* Do we have to worry about load factors?\n",
    "    * No\n",
    "* Can we assume inputs are valid or do we have to validate them?\n",
    "    * Assume they're valid\n",
    "* Can we assume this fits memory?\n",
    "    * Yes"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Solution"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Overwriting hash_map.py\n"
     ]
    }
   ],
   "source": [
    "%%writefile hash_map.py\n",
    "class Item(object):\n",
    "\n",
    "    def __init__(self, key, value):\n",
    "        self.key = key\n",
    "        self.value = value\n",
    "\n",
    "\n",
    "class HashTable(object):\n",
    "\n",
    "    def __init__(self, size):\n",
    "        self.size = size\n",
    "        self.table = [[] for _ in range(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",
    "        raise KeyError('Key not found')\n",
    "\n",
    "    def remove(self, key):\n",
    "        hash_index = self._hash_function(key)\n",
    "        for index, item in enumerate(self.table[hash_index]):\n",
    "            if item.key == key:\n",
    "                del self.table[hash_index][index]\n",
    "                return\n",
    "        raise KeyError('Key not found')"
   ]
  }
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