Longest Common Substring

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Your question is Longest Common Substring. Start with the requirements on the right.

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Problem

Given two strings s1 and s2, return the longest common substring shared by both strings. A substring must be contiguous in each string. If multiple answers have the same maximum length, return the one that appears first in s1.

Formal Specification

Write a function that takes two strings and returns a string.

Input: s1, s2, two lowercase or mixed-case ASCII strings
Output: the longest common substring between s1 and s2
If no common substring exists, return an empty string

Constraints

1 <= len(s1), len(s2) <= 2000
Strings may contain letters, digits, spaces, or punctuation
Return the earliest occurrence in s1 if multiple substrings share the maximum length

Function Signature

def longest_common_substring(s1, s2):

Your solutionPython 3

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