Add knapsack 01 challenge

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Donne Martin 2017-03-28 05:06:47 -04:00
parent 734d3385f6
commit 67f4ea99b4
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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/interactive-coding-challenges)."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"# Challenge Notebook"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Problem: Given a knapsack with a total weight capacity and a list of items with weight w(i) and value v(i), determine which items to select to maximize total value.\n",
"\n",
"* [Constraints](#Constraints)\n",
"* [Test Cases](#Test-Cases)\n",
"* [Algorithm](#Algorithm)\n",
"* [Code](#Code)\n",
"* [Unit Test](#Unit-Test)\n",
"* [Solution Notebook](#Solution-Notebook)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Constraints\n",
"\n",
"* Can we replace the items once they are placed in the knapsack?\n",
" * No, this is the 0/1 knapsack problem\n",
"* Can we split an item?\n",
" * No\n",
"* Can we get an input item with weight of 0 or value of 0?\n",
" * No\n",
"* Can we assume the inputs are valid?\n",
" * No\n",
"* Are the inputs in sorted order by val/weight?\n",
" * Yes, if not we'd need to sort them first\n",
"* Can we assume this fits memory?\n",
" * Yes"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Test Cases\n",
"\n",
"* items or total weight is None -> Exception\n",
"* items or total weight is 0 -> 0\n",
"* General case\n",
"\n",
"<pre>\n",
"total_weight = 8\n",
"items\n",
" v | w\n",
" 0 | 0\n",
"a 2 | 2\n",
"b 4 | 2\n",
"c 6 | 4\n",
"d 9 | 5\n",
"\n",
"max value = 13\n",
"items\n",
" v | w\n",
"b 4 | 2\n",
"d 9 | 5 \n",
"</pre>"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Algorithm\n",
"\n",
"Refer to the [Solution Notebook](). If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Code"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {
"collapsed": true
},
"outputs": [],
"source": [
"class Item(object):\n",
"\n",
" def __init__(self, label, value, weight):\n",
" self.label = label\n",
" self.value = value\n",
" self.weight = weight\n",
"\n",
" def __repr__(self):\n",
" return self.label + ' v:' + str(self.value) + ' w:' + str(self.weight)"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {
"collapsed": false
},
"outputs": [],
"source": [
"class Knapsack(object):\n",
"\n",
" def fill_knapsack(self, input_items, total_weight):\n",
" # TODO: Implement me\n",
" pass"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Unit Test"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**The following unit test is expected to fail until you solve the challenge.**"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {
"collapsed": false
},
"outputs": [],
"source": [
"# %load test_knapsack.py\n",
"from nose.tools import assert_equal, assert_raises\n",
"\n",
"\n",
"class TestKnapsack(object):\n",
"\n",
" def test_knapsack_bottom_up(self):\n",
" knapsack = Knapsack()\n",
" assert_raises(TypeError, knapsack.fill_knapsack, None, None)\n",
" assert_equal(knapsack.fill_knapsack(0, 0), 0)\n",
" items = []\n",
" items.append(Item(label='a', value=2, weight=2))\n",
" items.append(Item(label='b', value=4, weight=2))\n",
" items.append(Item(label='c', value=6, weight=4))\n",
" items.append(Item(label='d', value=9, weight=5))\n",
" total_weight = 8\n",
" expected_value = 13\n",
" results = knapsack.fill_knapsack(items, total_weight)\n",
" assert_equal(results[0].label, 'd')\n",
" assert_equal(results[1].label, 'b')\n",
" total_value = 0\n",
" for item in results:\n",
" total_value += item.value\n",
" assert_equal(total_value, expected_value)\n",
" print('Success: test_knapsack_bottom_up')\n",
"\n",
" def test_knapsack_top_down(self):\n",
" knapsack = KnapsackTopDown()\n",
" assert_raises(TypeError, knapsack.fill_knapsack, None, None)\n",
" assert_equal(knapsack.fill_knapsack(0, 0), 0)\n",
" items = []\n",
" items.append(Item(label='a', value=2, weight=2))\n",
" items.append(Item(label='b', value=4, weight=2))\n",
" items.append(Item(label='c', value=6, weight=4))\n",
" items.append(Item(label='d', value=9, weight=5))\n",
" total_weight = 8\n",
" expected_value = 13\n",
" assert_equal(knapsack.fill_knapsack(items, total_weight), expected_value)\n",
" print('Success: test_knapsack_top_down')\n",
"\n",
"def main():\n",
" test = TestKnapsack()\n",
" test.test_knapsack_bottom_up()\n",
" test.test_knapsack_top_down()\n",
"\n",
"\n",
"if __name__ == '__main__':\n",
" main()"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Solution Notebook\n",
"\n",
"Review the [Solution Notebook]() for a discussion on algorithms and code solutions."
]
}
],
"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": "3.5.0"
}
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"nbformat": 4,
"nbformat_minor": 0
}

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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/interactive-coding-challenges)."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"# Solution Notebook"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Problem: Given a knapsack with a total weight capacity and a list of items with weight w(i) and value v(i), determine which items to select to maximize total value.\n",
"\n",
"* [Constraints](#Constraints)\n",
"* [Test Cases](#Test-Cases)\n",
"* [Algorithm](#Algorithm)\n",
"* [Code](#Code)\n",
"* [Unit Test](#Unit-Test)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Constraints\n",
"\n",
"* Can we replace the items once they are placed in the knapsack?\n",
" * No, this is the 0/1 knapsack problem\n",
"* Can we split an item?\n",
" * No\n",
"* Can we get an input item with weight of 0 or value of 0?\n",
" * No\n",
"* Can we assume the inputs are valid?\n",
" * No\n",
"* Are the inputs in sorted order by val/weight?\n",
" * Yes, if not we'd need to sort them first\n",
"* Can we assume this fits memory?\n",
" * Yes"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Test Cases\n",
"\n",
"* items or total weight is None -> Exception\n",
"* items or total weight is 0 -> 0\n",
"* General case\n",
"\n",
"<pre>\n",
"total_weight = 8\n",
"items\n",
" v | w\n",
" 0 | 0\n",
"a 2 | 2\n",
"b 4 | 2\n",
"c 6 | 4\n",
"d 9 | 5\n",
"\n",
"max value = 13\n",
"items\n",
" v | w\n",
"b 4 | 2\n",
"d 9 | 5 \n",
"</pre>"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Algorithm\n",
"\n",
"We'll use bottom up dynamic programming to build a table.\n",
"\n",
"The solution for the top down approach is also provided below.\n",
"\n",
"<pre>\n",
"v = value\n",
"w = weight\n",
"\n",
" j \n",
" -------------------------------------------------\n",
" | v | w || 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |\n",
" -------------------------------------------------\n",
" | 0 | 0 || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |\n",
"i a | 2 | 2 || 0 | 0 | 2 | 2 | 2 | 2 | 2 | 2 | 2 |\n",
" b | 4 | 2 || 0 | 0 | 4 | 4 | 6 | 6 | 6 | 6 | 6 |\n",
" c | 6 | 4 || 0 | 0 | 4 | 4 | 6 | 6 | 10 | 10 | 12 |\n",
" d | 9 | 5 || 0 | 0 | 4 | 4 | 6 | 9 | 10 | 13 | 13 |\n",
" -------------------------------------------------\n",
"\n",
"i = row\n",
"j = col\n",
"\n",
"if j >= item[i].weight:\n",
" T[i][j] = max(item[i].value + T[i - 1][j - item[i].weight],\n",
" T[i - 1][j])\n",
"else:\n",
" T[i][j] = T[i - 1][j]\n",
"</pre>\n",
"\n",
"Complexity:\n",
"* Time: O(n * w), where n is the number of items and w is the total weight\n",
"* Space: O(n * w), where n is the number of items and w is the total weight"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Code"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### Item Class"
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {
"collapsed": true
},
"outputs": [],
"source": [
"class Item(object):\n",
"\n",
" def __init__(self, label, value, weight):\n",
" self.label = label\n",
" self.value = value\n",
" self.weight = weight\n",
"\n",
" def __repr__(self):\n",
" return self.label + ' v:' + str(self.value) + ' w:' + str(self.weight)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### Knapsack Bottom Up"
]
},
{
"cell_type": "code",
"execution_count": 2,
"metadata": {
"collapsed": false
},
"outputs": [],
"source": [
"class Knapsack(object):\n",
"\n",
" def fill_knapsack(self, input_items, total_weight):\n",
" if input_items is None or total_weight is None:\n",
" raise TypeError('input_items or total_weight cannot be None')\n",
" if not input_items or total_weight == 0:\n",
" return 0\n",
" items = list([Item(label='', value=0, weight=0)] + input_items)\n",
" num_rows = len(items)\n",
" num_cols = total_weight + 1\n",
" T = [[None] * num_cols for _ in range(num_rows)]\n",
" for i in range(num_rows):\n",
" for j in range(num_cols):\n",
" if i == 0 or j == 0:\n",
" T[i][j] = 0\n",
" elif j >= items[i].weight:\n",
" T[i][j] = max(items[i].value + T[i - 1][j - items[i].weight],\n",
" T[i - 1][j])\n",
" else:\n",
" T[i][j] = T[i - 1][j]\n",
" results = []\n",
" i = num_rows - 1\n",
" j = num_cols - 1\n",
" while T[i][j] != 0:\n",
" if T[i - 1][j] == T[i][j]:\n",
" i -= 1\n",
" elif T[i][j - 1] == T[i][j]:\n",
" j -= 1\n",
" else:\n",
" results.append(items[i])\n",
" i -= 1\n",
" j -= items[i].weight\n",
" return results"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### Knapsack Top Down"
]
},
{
"cell_type": "code",
"execution_count": 3,
"metadata": {
"collapsed": false
},
"outputs": [],
"source": [
"class KnapsackTopDown(object):\n",
"\n",
" def fill_knapsack(self, items, total_weight):\n",
" if items is None or total_weight is None:\n",
" raise TypeError('input_items or total_weight cannot be None')\n",
" if not items or not total_weight:\n",
" return 0\n",
" memo = {}\n",
" result = self._fill_knapsack(items, total_weight, memo, index=0)\n",
" return result\n",
"\n",
"\n",
" def _fill_knapsack(self, items, total_weight, memo, index):\n",
" if total_weight < 0:\n",
" return 0\n",
" if not total_weight or index >= len(items):\n",
" return items[index - 1].value\n",
" if (total_weight, len(items) - index - 1) in memo:\n",
" return memo[(total_weight, len(items) - index - 1)] + items[index - 1].value\n",
" results = []\n",
" for i in range(index, len(items)):\n",
" total_weight -= items[i].weight\n",
" result = self._fill_knapsack(items, total_weight, memo, index=i + 1)\n",
" total_weight += items[i].weight\n",
" results.append(result)\n",
" results_index = 0\n",
" for i in range(index, len(items)):\n",
" memo[total_weight, len(items) - i] = max(results[results_index:])\n",
" results_index += 1\n",
" return max(results) + (items[index - 1].value if index > 0 else 0)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### Knapsack Top Down Alternate"
]
},
{
"cell_type": "code",
"execution_count": 4,
"metadata": {
"collapsed": false
},
"outputs": [],
"source": [
"class Result(object):\n",
"\n",
" def __init__(self, total_weight, item):\n",
" self.total_weight = total_weight\n",
" self.item = item\n",
"\n",
" def __repr__(self):\n",
" return 'w:' + str(self.total_weight) + ' i:' + str(self.item)\n",
"\n",
" def __lt__(self, other):\n",
" return self.total_weight < other.total_weight\n",
"\n",
"\n",
"def knapsack_top_down_alt(items, total_weight):\n",
" if items is None or total_weight is None:\n",
" raise TypeError('input_items or total_weight cannot be None')\n",
" if not items or not total_weight:\n",
" return 0\n",
" memo = {}\n",
" result = _knapsack_top_down_alt(items, total_weight, memo, index=0)\n",
" curr_item = result.item\n",
" curr_weight = curr_item.weight\n",
" picked_items = [curr_item]\n",
" while curr_weight > 0:\n",
" total_weight -= curr_item.weight\n",
" curr_item = memo[(total_weight, len(items) - len(picked_items))].item\n",
" return result\n",
"\n",
"\n",
"def _knapsack_top_down_alt(items, total_weight, memo, index):\n",
" if total_weight < 0:\n",
" return Result(total_weight=0, item=None)\n",
" if not total_weight or index >= len(items):\n",
" return Result(total_weight=items[index - 1].value, item=items[index - 1])\n",
" if (total_weight, len(items) - index - 1) in memo:\n",
" weight=memo[(total_weight, \n",
" len(items) - index - 1)].total_weight + items[index - 1].value\n",
" return Result(total_weight=weight,\n",
" item=items[index-1])\n",
" results = []\n",
" for i in range(index, len(items)):\n",
" total_weight -= items[i].weight\n",
" result = _knapsack_top_down_alt(items, total_weight, memo, index=i + 1)\n",
" total_weight += items[i].weight\n",
" results.append(result)\n",
" results_index = 0\n",
" for i in range(index, len(items)):\n",
" memo[(total_weight, len(items) - i)] = max(results[results_index:])\n",
" results_index += 1\n",
" if index == 0:\n",
" result_item = memo[(total_weight, len(items) - 1)].item\n",
" else:\n",
" result_item = items[index - 1]\n",
" weight = max(results).total_weight + (items[index - 1].value if index > 0 else 0)\n",
" return Result(total_weight=weight,\n",
" item=result_item)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Unit Test"
]
},
{
"cell_type": "code",
"execution_count": 5,
"metadata": {
"collapsed": false
},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Overwriting test_knapsack.py\n"
]
}
],
"source": [
"%%writefile test_knapsack.py\n",
"from nose.tools import assert_equal, assert_raises\n",
"\n",
"\n",
"class TestKnapsack(object):\n",
"\n",
" def test_knapsack_bottom_up(self):\n",
" knapsack = Knapsack()\n",
" assert_raises(TypeError, knapsack.fill_knapsack, None, None)\n",
" assert_equal(knapsack.fill_knapsack(0, 0), 0)\n",
" items = []\n",
" items.append(Item(label='a', value=2, weight=2))\n",
" items.append(Item(label='b', value=4, weight=2))\n",
" items.append(Item(label='c', value=6, weight=4))\n",
" items.append(Item(label='d', value=9, weight=5))\n",
" total_weight = 8\n",
" expected_value = 13\n",
" results = knapsack.fill_knapsack(items, total_weight)\n",
" assert_equal(results[0].label, 'd')\n",
" assert_equal(results[1].label, 'b')\n",
" total_value = 0\n",
" for item in results:\n",
" total_value += item.value\n",
" assert_equal(total_value, expected_value)\n",
" print('Success: test_knapsack_bottom_up')\n",
"\n",
" def test_knapsack_top_down(self):\n",
" knapsack = KnapsackTopDown()\n",
" assert_raises(TypeError, knapsack.fill_knapsack, None, None)\n",
" assert_equal(knapsack.fill_knapsack(0, 0), 0)\n",
" items = []\n",
" items.append(Item(label='a', value=2, weight=2))\n",
" items.append(Item(label='b', value=4, weight=2))\n",
" items.append(Item(label='c', value=6, weight=4))\n",
" items.append(Item(label='d', value=9, weight=5))\n",
" total_weight = 8\n",
" expected_value = 13\n",
" assert_equal(knapsack.fill_knapsack(items, total_weight), expected_value)\n",
" print('Success: test_knapsack_top_down')\n",
"\n",
"def main():\n",
" test = TestKnapsack()\n",
" test.test_knapsack_bottom_up()\n",
" test.test_knapsack_top_down()\n",
"\n",
"\n",
"if __name__ == '__main__':\n",
" main()"
]
},
{
"cell_type": "code",
"execution_count": 6,
"metadata": {
"collapsed": false
},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Success: test_knapsack_bottom_up\n",
"Success: test_knapsack_top_down\n"
]
}
],
"source": [
"%run -i test_knapsack.py"
]
}
],
"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",
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from nose.tools import assert_equal, assert_raises
class TestKnapsack(object):
def test_knapsack_bottom_up(self):
knapsack = Knapsack()
assert_raises(TypeError, knapsack.fill_knapsack, None, None)
assert_equal(knapsack.fill_knapsack(0, 0), 0)
items = []
items.append(Item(label='a', value=2, weight=2))
items.append(Item(label='b', value=4, weight=2))
items.append(Item(label='c', value=6, weight=4))
items.append(Item(label='d', value=9, weight=5))
total_weight = 8
expected_value = 13
results = knapsack.fill_knapsack(items, total_weight)
assert_equal(results[0].label, 'd')
assert_equal(results[1].label, 'b')
total_value = 0
for item in results:
total_value += item.value
assert_equal(total_value, expected_value)
print('Success: test_knapsack_bottom_up')
def test_knapsack_top_down(self):
knapsack = KnapsackTopDown()
assert_raises(TypeError, knapsack.fill_knapsack, None, None)
assert_equal(knapsack.fill_knapsack(0, 0), 0)
items = []
items.append(Item(label='a', value=2, weight=2))
items.append(Item(label='b', value=4, weight=2))
items.append(Item(label='c', value=6, weight=4))
items.append(Item(label='d', value=9, weight=5))
total_weight = 8
expected_value = 13
assert_equal(knapsack.fill_knapsack(items, total_weight), expected_value)
print('Success: test_knapsack_top_down')
def main():
test = TestKnapsack()
test.test_knapsack_bottom_up()
test.test_knapsack_top_down()
if __name__ == '__main__':
main()