栈stack:栈区,后进先出LIFO结构。
ADT: data
method:push,pop
使用双端队列实现栈。deque模拟stack
class Node(object):
def __init__(self, value=None, prev=None, next=None):
self.value, self.prev, self.next = value, prev, next
class CircleDoubleLinedList(object):
def __init__(self, maxsize=None):
self.maxsize = maxsize
node = Node()
node.next, node.prev = node, node # 开始头节点和尾节点都指向node
self.root = node # root节点不计入长度
self.length = 0
def __len__(self):
return self.length
def headnode(self):
return self.root.next
def tailnode(self):
return self.root.prev
def append(self, value):
if self.maxsize is not None and len(self) > self.maxsize:
raise Exception("full")
node = Node(value=value)
tailnode = self.tailnode()
tailnode.next = node
node.prev = tailnode
node.next = self.root # 注意这里是根节点,不是头节点
self.root.prev = node
self.length += 1
def appendleft(self, value):
if self.maxsize is not None and len(self) > self.maxsize:
raise Exception("full")
node = Node(value=value)
if self.root.next is self.root: # empty
node.next = self.root
node.prev = self.root
self.root.next = node
self.root.prev = node
else:
node.prev = self.root
headnode = self.root.next
node.next = headnode
headnode.prev = node
self.root.next = node
self.length += 1
def remove(self, node): # 删除O(1)复杂度,传入的是node,不是值
if node is self.root:
return
else:
node.prev.next = node.next
node.next.prev = node.prev
self.length -= 1
return node
def iter_node(self):
"""遍历"""
if self.root.next is self.root:
return
curnode = self.root.next
while curnode.next is not self.root:
yield curnode
curnode = curnode.next
yield curnode
def __iter__(self):
for node in self.iter_node():
yield node.value
def iter_node_reverse(self):
if self.root.prev is self.root:
return
curnode = self.root.prev
while curnode.prev is not self.root:
yield curnode
curnode = curnode.prev
yield curnode
"""使用循环双端队列实现栈"""
class Deque(CircleDoubleLinedList):
def pop(self):
if len(self) == 0:
raise Exception('empty')
tailnode = self.tailnode()
value = tailnode.value
self.remove(tailnode)
return value
def popleft(self):
if len(self) == 0:
raise Exception("empty")
headnode = self.headnode()
value = headnode.value
self.remove(headnode)
return value
class Stack():
def __init__(self):
self.deque = Deque()
def push(self, value):
return self.deque.append(value)
def pop(self):
return self.deque.pop()
def __len__(self):
return len(self.deque)
def is_empty(self):
return len(self) == 0
def test_stack():
s = Stack()
for i in range(3):
s.push(i)
assert len(s) == 3
assert s.pop() == 2
assert s.pop() == 1
assert s.pop() == 0
assert s.is_empty()
import pytest
with pytest.raises(Exception) as excinfo:
s.pop()
assert 'empty' in str(excinfo.value)