Polish queue challenge and solution (#70)

Update constraints, algorithm discussion, and code.

stacks_queues/queue_list/queue_list.py

@@ -8,27 +8,28 @@ class Node(object):
 class Queue(object):
 
     def __init__(self):
-        self.first = None
+        self.head = None
-        self.last = None
+        self.tail = None
 
     def enqueue(self, data):
         node = Node(data)
-        if self.first is None and self.last is None:
+        # Empty list
-            self.first = node
+        if self.head is None and self.tail is None:
-            self.last = node
+            self.head = node
+            self.tail = node
         else:
-            self.last.next = node
+            self.tail.next = node
-            self.last = node
+            self.tail = node
 
     def dequeue(self):
         # Empty list
-        if self.first is None and self.last is None:
+        if self.head is None and self.tail is None:
             return None
-        data = self.first.data
+        data = self.head.data
         # Remove only element from a one element list
-        if self.first == self.last:
+        if self.head == self.tail:
-            self.first = None
+            self.head = None
-            self.last = None
+            self.tail = None
         else:
-            self.first = self.first.next
+            self.head = self.head.next
         return data

stacks_queues/queue_list/queue_list_challenge.ipynb

@@ -40,6 +40,8 @@
     "* If there are no items on the list, do you expect the first and last pointers to be None?\n",
     "    * Yes\n",
     "* If you dequeue on an empty queue, does that return None?\n",
+    "    * Yes\n",
+    "* Can we assume this fits memory?\n",
     "    * Yes"
    ]
   },
@@ -179,21 +181,21 @@
  ],
  "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",
+   "pygments_lexer": "ipython3",
-   "version": "2.7.10"
+   "version": "3.5.0"
   }
  },
  "nbformat": 4,

stacks_queues/queue_list/queue_list_solution.ipynb

@@ -34,11 +34,13 @@
    "source": [
     "## Constraints\n",
     "\n",
-    "* If there is one item in the list, do you expect the first and last pointers to both point to it?\n",
+    "* If there is one item in the list, do you expect the head and tail pointers to both point to it?\n",
     "    * Yes\n",
-    "* If there are no items on the list, do you expect the first and last pointers to be None?\n",
+    "* If there are no items on the list, do you expect the head and tail pointers to be None?\n",
     "    * Yes\n",
     "* If you dequeue on an empty queue, does that return None?\n",
+    "    * Yes\n",
+    "* Can we assume this fits memory?\n",
     "    * Yes"
    ]
   },
@@ -68,8 +70,8 @@
     "\n",
     "### Enqueue\n",
     "\n",
-    "* If the list is empty, set first and last to node\n",
+    "* If the list is empty, set head and tail to node\n",
-    "* Else, set last to node\n",
+    "* Else, set tail to node\n",
     "\n",
     "Complexity:\n",
     "* Time: O(1)\n",
@@ -79,12 +81,12 @@
     "\n",
     "* If the list is empty, return None\n",
     "* If the list has one node\n",
-    "    * Save the first node's value\n",
+    "    * Save the head node's value\n",
-    "    * Set first and last to None\n",
+    "    * Set head and tail to None\n",
     "    * Return the saved value\n",
     "* Else\n",
-    "    * Save the first node's value\n",
+    "    * Save the head node's value\n",
-    "    * Set first to its next node\n",
+    "    * Set head to its next node\n",
     "    * Return the saved value\n",
     "\n",
     "Complexity:\n",
@@ -126,29 +128,30 @@
     "class Queue(object):\n",
     "\n",
     "    def __init__(self):\n",
-    "        self.first = None\n",
+    "        self.head = None\n",
-    "        self.last = None\n",
+    "        self.tail = None\n",
     "\n",
     "    def enqueue(self, data):\n",
     "        node = Node(data)\n",
-    "        if self.first is None and self.last is None:\n",
+    "        # Empty list\n",
-    "            self.first = node\n",
+    "        if self.head is None and self.tail is None:\n",
-    "            self.last = node\n",
+    "            self.head = node\n",
+    "            self.tail = node\n",
     "        else:\n",
-    "            self.last.next = node\n",
+    "            self.tail.next = node\n",
-    "            self.last = node\n",
+    "            self.tail = node\n",
     "\n",
     "    def dequeue(self):\n",
     "        # Empty list\n",
-    "        if self.first is None and self.last is None:\n",
+    "        if self.head is None and self.tail is None:\n",
     "            return None\n",
-    "        data = self.first.data\n",
+    "        data = self.head.data\n",
     "        # Remove only element from a one element list\n",
-    "        if self.first == self.last:\n",
+    "        if self.head == self.tail:\n",
-    "            self.first = None\n",
+    "            self.head = None\n",
-    "            self.last = None\n",
+    "            self.tail = None\n",
     "        else:\n",
-    "            self.first = self.first.next\n",
+    "            self.head = self.head.next\n",
     "        return data"
    ]
   },
@@ -300,7 +303,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.4.3"
+   "version": "3.5.0"
   }
  },
  "nbformat": 4,