interactive-coding-challenges/arrays_strings/hash_map/hash_map_solution.ipynb
Donne Martin 9636459124 Update hash map challenge (#126)
Make hash_function private.
2016-11-30 07:16:44 -05:00

283 lines
7.3 KiB
Python

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"This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges)."
]
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{
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"metadata": {},
"source": [
"# Solution Notebook"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Problem: Implement a hash table with set, get, and remove methods.\n",
"\n",
"* [Constraints](#Constraints)\n",
"* [Test Cases](#Test-Cases)\n",
"* [Algorithm](#Algorithm)\n",
"* [Code](#Code)\n",
"* [Unit Test](#Unit-Test)"
]
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{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Constraints\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",
"* Do we have to validate inputs?\n",
" * No\n",
"* Can we assume this fits memory?\n",
" * Yes"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Test Cases\n",
"\n",
"* `get` no matching key -> KeyError exception\n",
"* `get` matching key -> value\n",
"* `set` no matchin gkey -> new key, value\n",
"* `set` matching key -> update value\n",
"* `remove` no matching key -> KeyError exception\n",
"* `remove` matching key -> remove key, value"
]
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"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, raise KeyError\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",
"* Else, raise KeyError\n",
"\n",
"Complexity:\n",
"* Time: O(1) average and best, O(n) worst\n",
"* Space: O(1)"
]
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{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Code"
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {
"collapsed": false
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"outputs": [],
"source": [
"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')"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Unit Test"
]
},
{
"cell_type": "code",
"execution_count": 2,
"metadata": {
"collapsed": false
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"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Overwriting test_hash_map.py\n"
]
}
],
"source": [
"%%writefile test_hash_map.py\n",
"from nose.tools import assert_equal, assert_raises\n",
"\n",
"\n",
"class TestHashMap(object):\n",
"\n",
" # TODO: It would be better if we had unit tests for each\n",
" # method in addition to the following end-to-end test\n",
" def test_end_to_end(self):\n",
" hash_table = HashTable(10)\n",
"\n",
" print(\"Test: get on an empty hash table index\")\n",
" assert_raises(KeyError, hash_table.get, 0)\n",
"\n",
" print(\"Test: set on an empty hash table index\")\n",
" hash_table.set(0, 'foo')\n",
" assert_equal(hash_table.get(0), 'foo')\n",
" hash_table.set(1, 'bar')\n",
" assert_equal(hash_table.get(1), 'bar')\n",
"\n",
" print(\"Test: set on a non empty hash table index\")\n",
" hash_table.set(10, 'foo2')\n",
" assert_equal(hash_table.get(0), 'foo')\n",
" assert_equal(hash_table.get(10), 'foo2')\n",
"\n",
" print(\"Test: set on a key that already exists\")\n",
" hash_table.set(10, 'foo3')\n",
" assert_equal(hash_table.get(0), 'foo')\n",
" assert_equal(hash_table.get(10), 'foo3')\n",
"\n",
" print(\"Test: remove on a key that already exists\")\n",
" hash_table.remove(10)\n",
" assert_equal(hash_table.get(0), 'foo')\n",
" assert_raises(KeyError, hash_table.get, 10)\n",
"\n",
" print(\"Test: remove on a key that doesn't exist\")\n",
" assert_raises(KeyError, hash_table.remove, -1)\n",
"\n",
" print('Success: test_end_to_end')\n",
"\n",
"\n",
"def main():\n",
" test = TestHashMap()\n",
" test.test_end_to_end()\n",
"\n",
"\n",
"if __name__ == '__main__':\n",
" main()"
]
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"Test: get on an empty hash table index\n",
"Test: set on an empty hash table index\n",
"Test: set on a non empty hash table index\n",
"Test: set on a key that already exists\n",
"Test: remove on a key that already exists\n",
"Test: remove on a key that doesn't exist\n",
"Success: test_end_to_end\n"
]
}
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"source": [
"run -i test_hash_map.py"
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