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20141125a

Implement a Stack class

Write a class that implements the stack data structure.

We want to use the class the following way:

s = Stack()       # create an empty stack
print(s)          # [
print(s.empty())  # True
s.push(1)
s.push(4)
s.push(5)
print(s)          # [1 4 5
print(s.size())   # 3
print(s.empty())  # False
x = s.pop()
print(x)          # 5
print(s)          # [1 4
s.pop()
s.pop()           # now it's empty
x = s.pop()
print(x)          # None (means that we wanted to take an element out of an empty stack)

Queue data structure

Now write a class that implements the queue data structure. First, think over what operations a queue should support. Then, write some examples (similarly to the code above), and finally implement the Queue class.

The implementation doesn't have to be efficient (yet).