By Harmanraj Singh Wadhwa (www.linkedin.com/in/hswadhwa)

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1. What are the variables used?

2. What is the data structures used?

3. What are the things inside the data structure?

4. What is the arrangement of the items inside the data structure?

# Representation invariant:
1.2. # _contents is a list of object.
3.   # _contents[:] are the objects in the deque.
4.   # if i < j, i >=0, j < len(_contents), then
     #    _contents[i] is to the left of _contents[j] in the deque
     #    _contents[j] is to the right of _contents[i] in the deque

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By Harmanraj Singh Wadhwa (www.linkedin.com/in/hswadhwa)