Longest Palindromic Substring in Python

Published on 26 October 2020 (Updated: 26 October 2020)

Welcome to the Longest Palindromic Substring in Python page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

``````import sys

errorMessage = "Usage: please provide a string that contains at least one palindrome"

def longestPalindrome(string):
longest = ""
string = string.lower()

centres = [len(string) - 1]
for diff in range(1, len(string)):
centres.append(centres[0] + diff)
centres.append(centres[0] - diff)

for centre in centres:
if (min(centre + 1, 2 * len(string) - 1 - centre) <= len(longest)):
break
if centre % 2 == 0:
left, right = (centre // 2) - 1, (centre // 2) + 1
else:
left, right = centre // 2, (centre // 2) + 1

while left >= 0 and right < len(
string) and string[left] == string[right]:
left -= 1
right += 1

if right - left > len(longest):
longest = string[left + 1:right]

return longest

if __name__ == '__main__':
if (len(sys.argv) < 2):
print(errorMessage)
else:
string = sys.argv[1]
if string == "" or string == None:
print(errorMessage)
sub = longestPalindrome(string)
if len(sub) == 1:
print(errorMessage)
else:
print(sub)

``````

Longest Palindromic Substring in Python was written by:

• izexi

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

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How to Run the Solution

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