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stack.py
50 lines (40 loc) · 1.14 KB
/
stack.py
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class Stack:
def __init__(self):
self.top = None
self.size = 0
def push(self, item):
p = Node(item)
if self.top is None:
self.top = p
else:
p.next = self.top
self.top = p
self.size += 1
def pop(self):
if self.is_empty():
raise ValueError('Popping off an empty stack.')
self.top = self.top.next
self.size -= 1
def peek(self):
if self.is_empty():
raise ValueError('Peeking into an empty stack.')
return self.top.data
def is_empty(self):
return self.top is None
def __sizeof__(self):
return self.size
def __repr__(self):
return "[{}]".format(", ".join(map(str, self)))
def __iter__(self):
current = self.top
while current is not None:
yield current
current = current.next
class Node:
def __init__(self, data):
if data is None:
raise ValueError('Cannot instantiate node with a None value.')
self.data = data
self.next = None
def __repr__(self):
return str(self.data)