Python Program to Find Longest Common Substring using Dynamic Programming with Bottom-Up Approach

When it is required to find longest common substring using dynamic programming with bottom-up approach, a method can be defined, that computes the solution to smaller problems. These smaller problem results don’t need to be computed again and again. Instead, they can just be accessed when required. This would lead to developing a solution to the bigger problem in hand.

Below is a demonstration for the same −

Example

 Live Demo

def compute_lcw(string_1, string_2):
   val = [[-1]*(len(string_2) + 1) for _ in range(len(string_1) + 1)]
   for i in range(len(string_1) + 1):
      val[i][len(string_2)] = 0
   for j in range(len(string_2)):
      val[len(string_1)][j] = 0
   lcw_i = lcw_j = -1
   lcw_len = 0
   for i in range(len(string_1) - 1, -1, -1):
      for j in range(len(string_2)):
         if string_1[i] != string_2[j]:
            val[i][j] = 0
         else:
            val[i][j] = 1 + val[i + 1][j + 1]
            if lcw_len < val[i][j]:
               lcw_len = val[i][j]
               lcw_i = i
               lcw_j = j
   return lcw_len, lcw_i, lcw_j
string_1 = 'bull'
string_2 = 'bullied'
lcw_len, lcw_i, lcw_j = compute_lcw(string_1, string_2)
print("The longest common substring is : ")
if lcw_len > 0:
   print(string_1[lcw_i:lcw_i + lcw_len])

Output

The longest common substring is :
bull

Explanation

• A method named ‘compute_lcw’ is defined, that takes two strings as parameter.
• The two strings are iterated over, and checked to see if any matching string is found in both of them.
• Even when a single character is found, it is stored in another variable.
• When this goes on until the end of the string, another string would be common to both these strings.
• Two strings are defined, and the method is called by passing these two strings.
• This operation’s data is assigned to a variable.
• It is then displayed as output on the console.

AmitDiwan

Updated on 11-Mar-2021 12:41:24

• Related Questions & Answers
• Program to find longest nice substring using Python
• Program to print the longest common substring using C++
• Program to find length of longest common substring in C++
• How to implement Fibonacci using bottom-up approach using C#?
• SequenceMatcher in Python for Longest Common Substring.
• Program to find longest awesome substring in Python
• How to implement coin change problem using bottom-up approach using C#?
• How to implement minimum step to one using bottom-up approach using C#?
• Difference Between Top-down and Bottom-up Approach
• C++ Program to Find Fibonacci Numbers using Dynamic Programming
• Program to find length of substring with consecutive common characters in Python
• Program to find length of longest palindromic substring in Python
• How to find the longest common substring from more than two strings in Python?
• Program to find length of longest substring with even vowel counts in Python
• C++ Program to Find Factorial of a Number using Dynamic Programming