class ListStack(object):
'''
Pushdown Stack(linked-list implmentation).
-------------
Stack(): init queue
push(item): push an item
pop(): remove the most recently added item
top(): get the most recently added item
empty = isEmpty(): tell stack is empty
stackSize = size(): get size of stack
clear(): reset the stack
'''
def __init__(self):
self.list = LinkedList()
def push(self, item):
self.list.addHead(item)
def isEmpty(self):
return self.list.isEmpty()
def pop(self):
if self.isEmpty():
return
self.list.remove(0)
def top(self):
if self.isEmpty():
return None
return self.list.get(0).item
def size(self):
return self.list.size()
def clear(self):
self.list = LinkedList()
