Polish set of stacks solution

stacks_queues/set_of_stacks/set_of_stacks_solution.ipynb

@@ -35,7 +35,7 @@
     "\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",
+    "* If a stack becomes full, should we automatically create one?\n",
     "    * Yes\n",
     "* If a stack becomes empty, should we delete it?\n",
     "    * Yes"
@@ -50,7 +50,7 @@
     "* 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"
+    "* Pop on a stack to destroy it"
    ]
   },
   {
@@ -67,7 +67,7 @@
     "\n",
     "Complexity:\n",
     "* Time: O(1)\n",
-    "* Space: O(1)\n",
+    "* Space: O(m), where m is the size of the new stack\n",
     "\n",
     "### Pop\n",
     "\n",
@@ -113,21 +113,19 @@
     "class StackWithCapacity(Stack):\n",
     "\n",
     "    def __init__(self, top=None, capacity=10):\n",
+    "        super(StackWithCapacity, self).__init__(top)\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",
+    "        if self.is_full():\n",
     "            raise Exception('Stack full')\n",
+    "        super(StackWithCapacity, self).push(data)\n",
+    "        self.num_items += 1\n",
     "\n",
     "    def pop(self):\n",
-    "        data = super(StackWithCapacity, self).pop()\n",
     "        self.num_items -= 1\n",
-    "        return data\n",
+    "        return super(StackWithCapacity, self).pop()\n",
     "\n",
     "    def is_full(self):\n",
     "        return self.num_items == self.capacity\n",
@@ -148,17 +146,13 @@
     "\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",
+    "            return None\n",
+    "        data = self.last_stack.pop()\n",
+    "        if self.last_stack.num_items == 0:\n",
     "            self.stacks.pop()\n",
+    "            self.last_stack = self.stacks[len(self.stacks)-1] \\\n",
+    "                if len(self.stacks) else None\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"
    ]
   },
@@ -194,8 +188,7 @@
     "\n",
     "    def test_set_of_stacks(self):\n",
     "        print('Test: Push on an empty stack')\n",
-    "        capacity = 2\n",
-    "        stacks = SetOfStacks(capacity)\n",
+    "        stacks = SetOfStacks(capacity=2)\n",
     "        stacks.push(3)\n",
     "\n",
     "        print('Test: Push on a non-empty stack')\n",
@@ -204,7 +197,7 @@
     "        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",
+    "        print('Test: Pop on a stack to destroy it')\n",
     "        assert_equal(stacks.pop(), 'a')\n",
     "\n",
     "        print('Test: Pop general case')\n",
@@ -240,7 +233,7 @@
       "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 on a stack to destroy it\n",
       "Test: Pop general case\n",
       "Test: Pop on no elements\n",
       "Success: test_set_of_stacks\n"
@@ -254,21 +247,21 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "Python 2",
+   "display_name": "Python 3",
    "language": "python",
-   "name": "python2"
+   "name": "python3"
   },
   "language_info": {
    "codemirror_mode": {
     "name": "ipython",
-    "version": 2
+    "version": 3
    },
    "file_extension": ".py",
    "mimetype": "text/x-python",
    "name": "python",
    "nbconvert_exporter": "python",
-   "pygments_lexer": "ipython2",
-   "version": "2.7.10"
+   "pygments_lexer": "ipython3",
+   "version": "3.4.3"
   }
  },
  "nbformat": 4,

stacks_queues/set_of_stacks/test_set_of_stacks.py

@@ -5,8 +5,7 @@ class TestSetOfStacks(object):
 
     def test_set_of_stacks(self):
         print('Test: Push on an empty stack')
-        capacity = 2
-        stacks = SetOfStacks(capacity)
+        stacks = SetOfStacks(capacity=2)
         stacks.push(3)
 
         print('Test: Push on a non-empty stack')
@@ -15,7 +14,7 @@ class TestSetOfStacks(object):
         print('Test: Push on a capacity stack to create a new one')
         stacks.push('a')
 
-        print('Test: Pop on a one element stack to destroy it')
+        print('Test: Pop on a stack to destroy it')
         assert_equal(stacks.pop(), 'a')
 
         print('Test: Pop general case')