First solution in Clear category for Double Substring by tom-tom
from itertools import groupby
return max((min(sum(g), shift) for shift in range(len(text))
for k, g in groupby(a == b for a, b in zip(text, text[shift:]))), default = 0)
if __name__ == '__main__':
#These "asserts" using only for self-checking and not necessary for auto-testing
assert double_substring('aaaa') == 2, "First"
assert double_substring('abc') == 0, "Second"
assert double_substring('aghtfghkofgh') == 3, "Third"
print('"Run" is good. How is "Check"?')
Aug. 11, 2017