class Stack(object):
def __init__(self):
self.data = []
def push(self, data):
self.data.append(data)
def pop(self):
if len(self.data) == 0:
return -1
else:
return self.data.pop()
def peek(self):
if len(self.data) == 0:
return -1
else:
return self.data[-1]
class Node:
def __init__(self,data):
self.data = data
self.head = None
class Stack(object):
def __init__(self):
self.head = None
def push(self, data):
newNode = Node(data)
newNode.next = self.head
self.head = newNode
def pop(self):
if self.head:
data = self.head.data
self.head = self.head.next
return data
else:
return -1
def peek(self):
if self.head:
data = self.head.data
return data
else:
return -1
def print(self):
cur = self.head
string = ""
while cur:
string += str(cur.data)
if cur.next:
string += "=>"
cur = cur.next
stack = Stack()
stack.push(1)
stack.push(2)
stack.push(3)
print(s.peek()) # 3
print(s.pop()) # 3
print(s.pop()) # 2
print(s.pop()) # 1
print(s.pop()) # -1