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,