Polish set of stacks challenge and solution (#73)

Update constraints, algorithm discussion, and code.

stacks_queues/set_of_stacks/set_of_stacks_challenge.ipynb

@@ -36,9 +36,15 @@
     "\n",
     "* Can we assume we already have a stack class that can be used for this problem?\n",
     "    * Yes\n",
+    "* Are all stack bound by the same capacity?\n",
+    "    * Yes\n",
     "* If a stack becomes full, should automatically create one?\n",
     "    * Yes\n",
     "* If a stack becomes empty, should we delete it?\n",
+    "    * Yes\n",
+    "* If we pop on an empty stack, should we return None?\n",
+    "    * Yes\n",
+    "* Can we assume this fits memory?\n",
     "    * Yes"
    ]
   },
@@ -111,7 +117,7 @@
     "\n",
     "class SetOfStacks(object):\n",
     "\n",
-    "    def __init__(self, capacity):\n",
+    "    def __init__(self, indiv_stack_capacity):\n",
     "        # TODO: Implement me\n",
     "        pass\n",
     "\n",
@@ -151,7 +157,7 @@
     "\n",
     "    def test_set_of_stacks(self):\n",
     "        print('Test: Push on an empty stack')\n",
-    "        stacks = SetOfStacks(capacity=2)\n",
+    "        stacks = SetOfStacks(indiv_stack_capacity=2)\n",
     "        stacks.push(3)\n",
     "\n",
     "        print('Test: Push on a non-empty stack')\n",
@@ -208,7 +214,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.4.3"
+   "version": "3.5.0"
   }
  },
  "nbformat": 4,

stacks_queues/set_of_stacks/set_of_stacks_solution.ipynb

@@ -35,9 +35,15 @@
     "\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, should we automatically create one?\n",
+    "* Are all stack bound by the same capacity?\n",
+    "    * Yes\n",
+    "* If a stack becomes full, should automatically create one?\n",
     "    * Yes\n",
     "* If a stack becomes empty, should we delete it?\n",
+    "    * Yes\n",
+    "* If we pop on an empty stack, should we return None?\n",
+    "    * Yes\n",
+    "* Can we assume this fits memory?\n",
     "    * Yes"
    ]
   },
@@ -67,7 +73,7 @@
     "\n",
     "Complexity:\n",
     "* Time: O(1)\n",
-    "* Space: O(m), where m is the size of the new stack\n",
+    "* Space: O(m), where m is the size of the new stack if the last stack is full\n",
     "\n",
     "### Pop\n",
     "\n",
@@ -133,14 +139,14 @@
     "\n",
     "class SetOfStacks(object):\n",
     "\n",
-    "    def __init__(self, capacity):\n",
-    "        self.capacity = capacity\n",
+    "    def __init__(self, indiv_stack_capacity):\n",
+    "        self.indiv_stack_capacity = indiv_stack_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.last_stack = StackWithCapacity(None, self.indiv_stack_capacity)\n",
     "            self.stacks.append(self.last_stack)\n",
     "        self.last_stack.push(data)\n",
     "\n",
@@ -148,11 +154,10 @@
     "        if self.last_stack is None:\n",
     "            return None\n",
     "        data = self.last_stack.pop()\n",
-    "        if self.last_stack.num_items == 0:\n",
+    "        if not self.last_stack.num_items:\n",
     "            self.stacks.pop()\n",
-    "            self.last_stack = self.stacks[len(self.stacks)-1] \\\n",
+    "            self.last_stack = self.stacks[-1] \\\n",
     "                if len(self.stacks) else None\n",
-    "            num_stacks = len(self.stacks)\n",
     "        return data"
    ]
   },
@@ -188,7 +193,7 @@
     "\n",
     "    def test_set_of_stacks(self):\n",
     "        print('Test: Push on an empty stack')\n",
-    "        stacks = SetOfStacks(capacity=2)\n",
+    "        stacks = SetOfStacks(indiv_stack_capacity=2)\n",
     "        stacks.push(3)\n",
     "\n",
     "        print('Test: Push on a non-empty stack')\n",
@@ -261,7 +266,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.4.3"
+   "version": "3.5.0"
   }
  },
  "nbformat": 4,

stacks_queues/set_of_stacks/test_set_of_stacks.py

@@ -5,7 +5,7 @@ class TestSetOfStacks(object):
 
     def test_set_of_stacks(self):
         print('Test: Push on an empty stack')
-        stacks = SetOfStacks(capacity=2)
+        stacks = SetOfStacks(indiv_stack_capacity=2)
         stacks.push(3)
 
         print('Test: Push on a non-empty stack')