'''
Given an array:

[a_1, a_2, ..., a_N, b_1, b_2, ..., b_N, c_1, c_2, ..., c_N ]

convert it to:

[a_1, b_1, c_1, a_2, b_2, c_2, ..., a_N, b_N, c_N]

in-place using constant extra space.
'''

Create ConvertArray.py