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stack.py
46 lines (35 loc) · 985 Bytes
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stack.py
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class Node(object):
def __init__(self, data, nxt=None):
self.data = data
self.nxt = nxt
def __str__(self):
return self.data
class Stack(object):
def __init__(self):
self.top = None
def push(self, data):
node = Node(data)
if self.top is None:
self.top = node
else:
node.nxt = self.top
self.top = node
def pop(self):
if self.top is None:
raise AssertionError("Stack is empty")
val = self.top.data
self.top = self.top.nxt
return val
def peek(self):
return self.top.data if self.top else None
def __str__(self):
curr = self.top
string = ""
while curr is not None:
string += "{}".format(curr.data)
if curr.nxt is not None:
string += "->"
curr = curr.nxt
return string
def isEmpty(self):
return self.top is None