interactive-coding-challenges/stacks_queues/set_of_stacks/set_of_stacks.ipynb

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    "<small><i>This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://bit.ly/code-notes).</i></small>"
   ]
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    "## Problem: Implement SetOfStacks that wraps a list of stacks, where each stack is bound by a capacity.\n",
    "\n",
    "* [Constraints and Assumptions](#Constraints-and-Assumptions)\n",
    "* [Test Cases](#Test-Cases)\n",
    "* [Algorithm](#Algorithm)\n",
    "* [Code](#Code)\n",
    "* [Unit Test](#Unit-Test)"
   ]
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   "source": [
    "## Constraints\n",
    "\n",
    "*Problem statements are often intentionally ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
    "\n",
    "* Can we assume we already have a stack class that can be used for this problem?\n",
    "    * Yes\n",
    "* If a stack becomes full, we should automatically create one?\n",
    "    * Yes\n",
    "* If a stack becomes empty, should we delete it?\n",
    "    * Yes"
   ]
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   "source": [
    "## Test Cases\n",
    "\n",
    "* Push and pop on an empty stack\n",
    "* Push and pop on a non-empty stack\n",
    "* Push on a capacity stack to create a new one\n",
    "* Pop on a one element stack to destroy it"
   ]
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   "source": [
    "## Algorithm\n",
    "\n",
    "### Push\n",
    "\n",
    "* If there are no stacks or the last stack is full\n",
    "    * Create a new stack\n",
    "* Push to the new stack\n",
    "\n",
    "Complexity:\n",
    "* Time: O(1)\n",
    "* Space: O(1)\n",
    "\n",
    "### Pop\n",
    "\n",
    "* If there are no stacks, return None\n",
    "* Else if the last stack has one element\n",
    "    * Pop the last element's data\n",
    "    * Delete the now empty stack\n",
    "    * Update the last stack pointer\n",
    "* Else Pop the last element's data\n",
    "* Return the last element's data\n",
    "\n",
    "Complexity:\n",
    "* Time: O(1)\n",
    "* Space: O(1)"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
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  {
   "cell_type": "code",
   "execution_count": 1,
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   "source": [
    "%run stack.py"
   ]
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    "class StackWithCapacity(Stack):\n",
    "    def __init__(self, top=None, capacity=10):\n",
    "        self.capacity = capacity\n",
    "        self.num_items = 0\n",
    "        super(StackWithCapacity, self).__init__(top)\n",
    "\n",
    "    def push(self, data):\n",
    "        if self.num_items < self.capacity:\n",
    "            super(StackWithCapacity, self).push(data)\n",
    "            self.num_items += 1\n",
    "        else:\n",
    "            raise Exception('Stack full')\n",
    "\n",
    "    def pop(self):\n",
    "        data = super(StackWithCapacity, self).pop()\n",
    "        self.num_items -= 1\n",
    "        return data\n",
    "\n",
    "    def is_full(self):\n",
    "        return self.num_items == self.capacity\n",
    "\n",
    "class SetOfStacks(object):\n",
    "    def __init__(self, capacity):\n",
    "        self.capacity = capacity\n",
    "        self.stacks = []\n",
    "        self.last_stack = None\n",
    "\n",
    "    def push(self, data):\n",
    "        if self.last_stack is None or self.last_stack.is_full():\n",
    "            self.last_stack = StackWithCapacity(None, self.capacity)\n",
    "            self.stacks.append(self.last_stack)\n",
    "        self.last_stack.push(data)\n",
    "\n",
    "    def pop(self):\n",
    "        if self.last_stack is None:\n",
    "            return\n",
    "        elif self.last_stack.top.next is None:\n",
    "            data = self.last_stack.pop()\n",
    "            self.stacks.pop()\n",
    "            num_stacks = len(self.stacks)\n",
    "            if num_stacks == 0:\n",
    "                self.last_stack = None\n",
    "            else:\n",
    "                self.last_stack = self.stacks[num_stacks-1]\n",
    "        else:\n",
    "            data = self.last_stack.pop()\n",
    "        return data"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Unit Test\n",
    "\n",
    "*It is important to identify and run through general and edge cases from the [Test Cases](#Test-Cases) section by hand.  You generally will not be asked to write a unit test like what is shown below.*"
   ]
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   "cell_type": "code",
   "execution_count": 3,
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     "text": [
      "Test: Push on an empty stack\n",
      "Test: Push on a non-empty stack\n",
      "Test: Push on a capacity stack to create a new one\n",
      "Test: Pop on a one element stack to destroy it\n",
      "Test: Pop general case\n",
      "Test: Pop on no elements\n",
      "Success: test_set_of_stacks\n"
     ]
    }
   ],
   "source": [
    "from nose.tools import assert_equal\n",
    "\n",
    "class Test(object):\n",
    "    def test_set_of_stacks(self):\n",
    "        print('Test: Push on an empty stack')\n",
    "        capacity = 2\n",
    "        stacks = SetOfStacks(capacity)\n",
    "        stacks.push(3)\n",
    "\n",
    "        print('Test: Push on a non-empty stack')\n",
    "        stacks.push(5)\n",
    "\n",
    "        print('Test: Push on a capacity stack to create a new one')\n",
    "        stacks.push('a')\n",
    "\n",
    "        print('Test: Pop on a one element stack to destroy it')\n",
    "        assert_equal(stacks.pop(), 'a')\n",
    "\n",
    "        print('Test: Pop general case')\n",
    "        assert_equal(stacks.pop(), 5)\n",
    "        assert_equal(stacks.pop(), 3)\n",
    "\n",
    "        print('Test: Pop on no elements')\n",
    "        assert_equal(stacks.pop(), None)\n",
    "        \n",
    "        print('Success: test_set_of_stacks')\n",
    "\n",
    "if __name__ == '__main__':\n",
    "    test = Test()\n",
    "    test.test_set_of_stacks()"
   ]
  }
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