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Polish queue challenge and solution (#70)

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Update constraints, algorithm discussion, and code.
This commit is contained in:
Donne Martin 2016-06-19 20:08:26 -04:00 committed by GitHub
parent 4cdb85e22d
commit 0d20ff5931
3 changed files with 46 additions and 40 deletions
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27
stacks_queues/queue_list/queue_list.py
View File

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

12
stacks_queues/queue_list/queue_list_challenge.ipynb
View File

@ -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",
"version": "2.7.10"
"pygments_lexer": "ipython3",
"version": "3.5.0"
}
},
"nbformat": 4,

47
stacks_queues/queue_list/queue_list_solution.ipynb
View File

@ -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",
"* Else, set last to node\n",
"* If the list is empty, set head and tail 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",
" * Set first and last to None\n",
" * Save the head node's value\n",
" * Set head and tail to None\n",
" * Return the saved value\n",
"* Else\n",
" * Save the first node's value\n",
" * Set first to its next node\n",
" * Save the head node's value\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.last = None\n",
" self.head = 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",
" self.first = node\n",
" self.last = node\n",
" # Empty list\n",
" if self.head is None and self.tail is None:\n",
" self.head = node\n",
" self.tail = node\n",
" else:\n",
" self.last.next = node\n",
" self.last = node\n",
" self.tail.next = 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",
" self.first = None\n",
" self.last = None\n",
" if self.head == self.tail:\n",
" self.head = 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,