mirror of
https://github.com/TheAlgorithms/Python.git
synced 2024-12-05 02:40:16 +00:00
64 lines
1.9 KiB
Python
64 lines
1.9 KiB
Python
"""
|
|
Longest Common Substring Problem Statement: Given two sequences, find the
|
|
longest common substring present in both of them. A substring is
|
|
necessarily continuous.
|
|
Example: "abcdef" and "xabded" have two longest common substrings, "ab" or "de".
|
|
Therefore, algorithm should return any one of them.
|
|
"""
|
|
|
|
|
|
def longest_common_substring(text1: str, text2: str) -> str:
|
|
"""
|
|
Finds the longest common substring between two strings.
|
|
>>> longest_common_substring("", "")
|
|
''
|
|
>>> longest_common_substring("a","")
|
|
''
|
|
>>> longest_common_substring("", "a")
|
|
''
|
|
>>> longest_common_substring("a", "a")
|
|
'a'
|
|
>>> longest_common_substring("abcdef", "bcd")
|
|
'bcd'
|
|
>>> longest_common_substring("abcdef", "xabded")
|
|
'ab'
|
|
>>> longest_common_substring("GeeksforGeeks", "GeeksQuiz")
|
|
'Geeks'
|
|
>>> longest_common_substring("abcdxyz", "xyzabcd")
|
|
'abcd'
|
|
>>> longest_common_substring("zxabcdezy", "yzabcdezx")
|
|
'abcdez'
|
|
>>> longest_common_substring("OldSite:GeeksforGeeks.org", "NewSite:GeeksQuiz.com")
|
|
'Site:Geeks'
|
|
>>> longest_common_substring(1, 1)
|
|
Traceback (most recent call last):
|
|
...
|
|
ValueError: longest_common_substring() takes two strings for inputs
|
|
"""
|
|
|
|
if not (isinstance(text1, str) and isinstance(text2, str)):
|
|
raise ValueError("longest_common_substring() takes two strings for inputs")
|
|
|
|
text1_length = len(text1)
|
|
text2_length = len(text2)
|
|
|
|
dp = [[0] * (text2_length + 1) for _ in range(text1_length + 1)]
|
|
ans_index = 0
|
|
ans_length = 0
|
|
|
|
for i in range(1, text1_length + 1):
|
|
for j in range(1, text2_length + 1):
|
|
if text1[i - 1] == text2[j - 1]:
|
|
dp[i][j] = 1 + dp[i - 1][j - 1]
|
|
if dp[i][j] > ans_length:
|
|
ans_index = i
|
|
ans_length = dp[i][j]
|
|
|
|
return text1[ans_index - ans_length : ans_index]
|
|
|
|
|
|
if __name__ == "__main__":
|
|
import doctest
|
|
|
|
doctest.testmod()
|