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8-line py3 solution with explaination solution in Clear category for The Longest Palindromic by imhuwq
def longest_palindromic(text):
"""We check the sub strings of the text,
from longer to shorter, from left to right.
if any of these substring satisfies the condition of
substring == substring[::-1],
then we stop checking shorter sub strings,
and return this substring
"""
length = len(text)
# we loop through the text, from index 0 to index length-1
for i in range(length):
# sub_count indicates the count of sub strings in this period of loop
# for example, while i==0, count of sub strings will be 1
# and while i == 1, count be 2
sub_count = i + 1
# get the sub strings
for count in range(sub_count):
# the length of the substring become shorter while we keep looping
# and that's why we substract i
sub = text[count:count + length - i]
if sub == sub[::-1]:
return sub
return None
if __name__ == '__main__':
assert longest_palindromic("artrartrt") == "rtrartr", "The Longest"
assert longest_palindromic("abacada") == "aba", "The First"
assert longest_palindromic("aaaa") == "aaaa", "The A"
June 1, 2016
