SequenceMatcher in Python for Longest Common Substring
Given two strings ‘X’ and ‘Y’, print the longest common sub-string. Examples:
Input : X = "GeeksforGeeks",
Y = "GeeksQuiz"
Output : Geeks
Input : X = "zxabcdezy",
Y = "yzabcdezx"
Output : abcdezWe have existing solution for this problem please refer Print the longest common substring link. We will solve problem in python using SequenceMatcher.find_longest_match() method.
How SequenceMatcher.find_longest_match(aLow,aHigh,bLow,bHigh) method works ?
First we initialize SequenceMatcher object with two input string str1 and str2, find_longest_match(aLow,aHigh,bLow,bHigh) takes 4 parameters aLow, bLow are start index of first and second string respectively and aHigh, bHigh are length of first and second string respectively. find_longest_match() returns named tuple (i, j, k) such that a[i:i+k] is equal to b[j:j+k], if no blocks match, this returns (aLow, bLow, 0).
Implementation:
Python3
# Function to find Longest Common Sub-stringfrom difflib import SequenceMatcherdef longestSubstring(str1,str2): # initialize SequenceMatcher object with # input string seqMatch = SequenceMatcher(None,str1,str2) # find match of longest sub-string # output will be like Match(a=0, b=0, size=5) match = seqMatch.find_longest_match(0, len(str1), 0, len(str2)) # print longest substring if (match.size!=0): print (str1[match.a: match.a + match.size]) else: print ('No longest common sub-string found')# Driver programif __name__ == "__main__": str1 = 'GeeksforGeeks' str2 = 'GeeksQuiz' longestSubstring(str1,str2) |
Output
Geeks
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