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Added notebook solving the following: Sort a stack using another stack as a buffer.
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@ -39,6 +39,7 @@ Continually updated IPython Notebooks containing coding problems and solutions (
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* [Implement a set of stacks class 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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* [Implement a set of stacks class 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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* [Implement the Towers of Hanoi with 3 towers and N disks](http://nbviewer.ipython.org/github/donnemartin/algorithms-data-structures/blob/master/stacks-queues/hanoi.ipynb)
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* [Implement the Towers of Hanoi with 3 towers and N disks](http://nbviewer.ipython.org/github/donnemartin/algorithms-data-structures/blob/master/stacks-queues/hanoi.ipynb)
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* [Implement a queue using two stacks](http://nbviewer.ipython.org/github/donnemartin/algorithms-data-structures/blob/master/stacks-queues/queue-from-stacks.ipynb)
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* [Implement a queue using two stacks](http://nbviewer.ipython.org/github/donnemartin/algorithms-data-structures/blob/master/stacks-queues/queue-from-stacks.ipynb)
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* [Sort a stack using another stack as a buffer](http://nbviewer.ipython.org/github/donnemartin/algorithms-data-structures/blob/master/stacks-queues/sort-stack.ipynb)
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## Hacker Rank
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## Hacker Rank
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145
stacks-queues/sort-stack.ipynb
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145
stacks-queues/sort-stack.ipynb
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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: Sort a stack. You can use another stack as a buffer.\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)"
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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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"* When sorted, should the largest element be at the top or bottom?\n",
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" * Top\n",
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"* Can you have duplicate values, saw two 5s?\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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"* Empty stack\n",
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"* One element stack\n",
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"* Two or more element stack (general case)\n",
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"* Already sorted stack"
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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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"* Our buffer will hold elements in reverse sorted order, smallest at the top\n",
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"* Store the current top element in a temp variable\n",
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"* While stack is not empty\n",
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" * While buffer is empty or buffer top is > than temp\n",
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" * Move buffer top to stack\n",
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" * Move temp to top of buffer\n",
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"* Return buffer\n",
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"\n",
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"Complexity:\n",
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"* Time: O(n^2)\n",
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"* Space: O(n)"
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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 MyStack(Stack):\n",
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" def sort(self):\n",
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" buff = MyStack()\n",
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" while not self.is_empty():\n",
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" temp = self.pop()\n",
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" while not buff.is_empty() and buff.peek() > temp:\n",
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" self.push(buff.pop())\n",
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" buff.push(temp)\n",
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" return buff"
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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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"from random import randint\n",
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"\n",
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"def test_sort(num_items, stack=None):\n",
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" if stack is None:\n",
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" stack = MyStack()\n",
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" for _ in xrange(0, num_items):\n",
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" stack.push(randint(0, num_items))\n",
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" sorted_stack = stack.sort()\n",
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" for _ in xrange(0, num_items):\n",
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" print(sorted_stack.pop())\n",
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" return sorted_stack\n",
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"\n",
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"print('Empty stack')\n",
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"test_sort(0)\n",
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"print('One element stack')\n",
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"test_sort(1)\n",
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"print('Two or more element stack (general case)')\n",
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"sorted_stack = test_sort(5)"
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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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