Add Hash Table solution

solutions/object_oriented_design/hash_table/hash_map.ipynb

+{
+ "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-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')"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.4.3"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}
+%% Cell type:markdown id: tags:
+
+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-primer).
+
+%% Cell type:markdown id: tags:
+
+# Design a hash map
+
+%% Cell type:markdown id: tags:
+
+## Constraints and assumptions
+
+* For simplicity, are the keys integers only?
+    * Yes
+* For collision resolution, can we use chaining?
+    * Yes
+* Do we have to worry about load factors?
+    * No
+* Can we assume inputs are valid or do we have to validate them?
+    * Assume they're valid
+* Can we assume this fits memory?
+    * Yes
+
+%% Cell type:markdown id: tags:
+
+## Solution
+
+%% Cell type:code id: tags:
+
+``` python
+%%writefile hash_map.py
+class Item(object):
+
+    def __init__(self, key, value):
+        self.key = key
+        self.value = value
+
+
+class HashTable(object):
+
+    def __init__(self, size):
+        self.size = size
+        self.table = [[] for _ in range(self.size)]
+
+    def _hash_function(self, key):
+        return key % self.size
+
+    def set(self, key, value):
+        hash_index = self._hash_function(key)
+        for item in self.table[hash_index]:
+            if item.key == key:
+                item.value = value
+                return
+        self.table[hash_index].append(Item(key, value))
+
+    def get(self, key):
+        hash_index = self._hash_function(key)
+        for item in self.table[hash_index]:
+            if item.key == key:
+                return item.value
+        raise KeyError('Key not found')
+
+    def remove(self, key):
+        hash_index = self._hash_function(key)
+        for index, item in enumerate(self.table[hash_index]):
+            if item.key == key:
+                del self.table[hash_index][index]
+                return
+        raise KeyError('Key not found')
+```
+
+%%%% Output: stream
+
+    Overwriting hash_map.py

solutions/object_oriented_design/hash_table/hash_map.py

+class Item(object):
+
+    def __init__(self, key, value):
+        self.key = key
+        self.value = value
+
+
+class HashTable(object):
+
+    def __init__(self, size):
+        self.size = size
+        self.table = [[] for _ in range(self.size)]
+
+    def _hash_function(self, key):
+        return key % self.size
+
+    def set(self, key, value):
+        hash_index = self._hash_function(key)
+        for item in self.table[hash_index]:
+            if item.key == key:
+                item.value = value
+                return
+        self.table[hash_index].append(Item(key, value))
+
+    def get(self, key):
+        hash_index = self._hash_function(key)
+        for item in self.table[hash_index]:
+            if item.key == key:
+                return item.value
+        raise KeyError('Key not found')
+
+    def remove(self, key):
+        hash_index = self._hash_function(key)
+        for index, item in enumerate(self.table[hash_index]):
+            if item.key == key:
+                del self.table[hash_index][index]
+                return
+        raise KeyError('Key not found')
\ No newline at end of file