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Added notebook solving the following: Implement SetOfStacks that wraps a list of stacks, where each stack is bound by a capacity.
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Donne Martin
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@ -34,6 +34,7 @@ Continually updated IPython Notebooks containing coding problems and solutions (
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* [Implement a queue with enqueue and dequeue methods using a linked list](http://nbviewer.ipython.org/github/donnemartin/algorithms-data-structures/blob/master/stacks-queues/queue.ipynb)
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* [Implement n stacks using a single array](http://nbviewer.ipython.org/github/donnemartin/algorithms-data-structures/blob/master/stacks-queues/n-stacks.ipynb)
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* [Implement a stack that keeps track of its minimum element](http://nbviewer.ipython.org/github/donnemartin/algorithms-data-structures/blob/master/stacks-queues/stack-min.ipynb)
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* [Implement SetOfStacks that wraps a list of stacks, each bound by a capacity](http://nbviewer.ipython.org/github/donnemartin/algorithms-data-structures/blob/master/stacks-queues/set-of-stacks.ipynb)
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## License
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191
stacks-queues/set-of-stacks.ipynb
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191
stacks-queues/set-of-stacks.ipynb
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@ -0,0 +1,191 @@
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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 SetOfStacks that wraps a set of stacks bound by a capacity.\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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"* Can we assume we have a Stack class to use?\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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"* Push and pop on an empty stack\n",
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"* Push and pop on a non-empty stack\n",
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"* Push on a capacity stack to create a new one\n",
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"* Pop on a one element stack to destroy it"
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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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"### Push\n",
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"\n",
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"* If there are no stacks or the last stack is full\n",
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" * Create a new stack\n",
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"* Push to the new stack\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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"### Pop\n",
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"\n",
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"* If there are no stacks, return None\n",
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"* Else if the last stack has one element\n",
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" * Pop the last element's data\n",
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" * Delete the now empty stack\n",
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" * Update the last stack pointer\n",
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"* Else Pop the last element's data\n",
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"* Return the last element's data\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)"
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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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"%run stack.py"
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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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"class StackWithCapacity(Stack):\n",
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" def __init__(self, top=None, capacity=10):\n",
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" self.capacity = capacity\n",
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" self.num_items = 0\n",
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" super(StackWithCapacity, self).__init__(top)\n",
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"\n",
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" def push(self, data):\n",
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" if self.num_items < self.capacity:\n",
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" super(StackWithCapacity, self).push(data)\n",
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" self.num_items += 1\n",
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" else:\n",
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" raise Exception('Stack full')\n",
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"\n",
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" def pop(self):\n",
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" data = super(StackWithCapacity, self).pop()\n",
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" self.num_items -= 1\n",
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" return data\n",
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"\n",
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" def is_full(self):\n",
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" return self.num_items == self.capacity\n",
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"\n",
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"class SetOfStacks(object):\n",
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" def __init__(self, capacity):\n",
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" self.capacity = capacity\n",
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" self.stacks = []\n",
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" self.last_stack = None\n",
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"\n",
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" def push(self, data):\n",
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" if self.last_stack is None or self.last_stack.is_full():\n",
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" self.last_stack = StackWithCapacity(None, self.capacity)\n",
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" self.stacks.append(self.last_stack)\n",
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" self.last_stack.push(data)\n",
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"\n",
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" def pop(self):\n",
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" if self.last_stack is None:\n",
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" return\n",
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" elif self.last_stack.top.next is None:\n",
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" data = self.last_stack.pop()\n",
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" self.stacks.pop()\n",
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" num_stacks = len(self.stacks)\n",
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" if num_stacks == 0:\n",
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" self.last_stack = None\n",
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" else:\n",
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" self.last_stack = self.stacks[num_stacks-1]\n",
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" else:\n",
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" data = self.last_stack.pop()\n",
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" return data"
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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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"print('Push on an empty stack')\n",
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"capacity = 2\n",
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"stacks = SetOfStacks(capacity)\n",
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"stacks.push(3)\n",
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"print('Push on a non-empty stack')\n",
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"stacks.push(5)\n",
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"print('Push on a capacity stack to create a new one')\n",
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"stacks.push('a')\n",
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"print('Pop on a one element stack to destroy it')\n",
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"print(stacks.pop())\n",
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"print('Pop general case')\n",
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"print(stacks.pop())\n",
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"print(stacks.pop())\n",
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"print('Pop on no elements')\n",
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"print(stacks.pop())"
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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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