Python: Find the longest common sub-string from two given strings

Last update on April 19 2025 13:05:10 (UTC/GMT +8 hours)

Find longest common substring.

Write a Python program to find the longest common sub-string from two given strings.

Visual Presentation:

Sample Solution:

Python Code:

# Import SequenceMatcher from difflib
from difflib import SequenceMatcher

# Function to find longest common substring
def longest_Substring(s1,s2):

  # Create sequence matcher object
  seq_match = SequenceMatcher(None,s1,s2) 
  
  # Find longest matching substring
  match = seq_match.find_longest_match(0, len(s1), 0, len(s2))

  # If match found, return substring
  if (match.size!=0):  
    return (s1[match.a: match.a + match.size])
  
  # Else no match found
  else:
    return ('Longest common sub-string not present')

# Test strings  
s1 = 'abcdefgh'
s2 = 'xswerabcdwd'

# Print original strings 
print("Original Substrings:\n",s1+"\n",s2)

# Print message  
print("\nCommon longest sub_string:")

# Print longest common substring
print(longest_Substring(s1,s2)) 

Sample Output:

Original Substrings:
 abcdefgh
 xswerabcdwd

Common longest sub_string:
abcd
Original Substrings:
 abcdefgh
 xswerabcdwd

Common longest sub_string:
abcd

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Python program to find the longest common substring between two strings using dynamic programming.
• Write a Python program to implement a function that returns the longest common contiguous sequence shared by two strings.
• Write a Python program to use recursion or iterative methods to compute the longest common substring of two inputs.
• Write a Python program to build a 2D table for substring lengths and output the longest common substring from two strings.

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