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