The idea is to keep an inbox and outbox using stacks. Here is a simple implementation.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
| class Queue(object):
def __init__(self):
self._inbox = Stack()
self._outbox = Stack()
def _refill(self):
if not self._outbox:
while self._inbox:
self._outbox.push(self._inbox.pop())
def peek(self):
self._refill()
try:
return self._outbox.peek()
except IndexError:
raise EmptyQueueError()
def pop(self):
self._refill()
try:
retval = self._outbox.pop()
except IndexError:
raise EmptyQueueError()
else:
return retval
def push(self, value):
self._inbox.push(value)
class Stack():
def __init__(self, iterable=None):
self._data = [] if iterable is None else list(iterable)
def __bool__(self):
return bool(self._data)
def peek(self):
return self._data[-1]
def pop(self):
return self._data.pop()
def push(self, value):
self._data.append(value)
class EmptyQueueError(BaseException):
pass
|