Using visited as a default arg in graph and adding more deque use cases

[sbalasa]

[sbalasa]

But I've already used it in the same way

[chmnrathee]

@sbalasa --

Use python markdown syntax like below : (Start with three back-ticks python and end up with only three back-ticks )

# Code
s = "Python syntax highlighting"
print(s)
'''
# output
Python syntax highlighting
'''

instead of

''' deque([6, 7, 8, 9, 10], maxlen=5) 6 7 8 9 10 '''