Java Program to Implement Longest Common Substring Algorithm

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This is a Java Program to implement Longest Common Substring Algorithm. This program finds the longest common substring between two strings.

Here is the source code of the Java Program to implement Longest Common Substring Algorithm. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

  1. /**
  2.  ** Java Program to implement Longest Common Substring Algorithm
  3.  **/
  4.  
  5. import java.io.BufferedReader;
  6. import java.io.InputStreamReader;
  7. import java.io.IOException;
  8.  
  9. /** Class  LongestCommonSubstring **/
  10. public class  LongestCommonSubstring
  11. {
  12.     /** function lcs **/
  13.     public String lcs(String str1, String str2)
  14.     {
  15.         int l1 = str1.length();
  16.         int l2 = str2.length();
  17.  
  18.         int[][] arr = new int[l1 + 1][l2 + 1];
  19.         int len = 0, pos = -1;
  20.  
  21.         for (int x = 1; x < l1 + 1; x++)
  22.         {
  23.             for (int y = 1; y < l2 + 1; y++)
  24.             {
  25.                 if (str1.charAt(x - 1) == str2.charAt(y - 1))
  26.                 {
  27.                         arr[x][y] = arr[x - 1][y - 1] + 1;
  28.                         if (arr[x][y] > len)
  29.                         {
  30.                             len = arr[x][y];
  31.                             pos = x;
  32.                         }               
  33.                 }
  34.                 else
  35.                     arr[x][y] = 0;
  36.             }
  37.         }        
  38.  
  39.         return str1.substring(pos - len, pos);
  40.     }
  41.  
  42.     /** Main Function **/
  43.     public static void main(String[] args) throws IOException
  44.     {    
  45.         BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
  46.         System.out.println("Longest Common Substring Algorithm Test\n");
  47.  
  48.         System.out.println("\nEnter string 1");
  49.         String str1 = br.readLine();
  50.  
  51.         System.out.println("\nEnter string 2");
  52.         String str2 = br.readLine();
  53.  
  54.         LongestCommonSubstring obj = new LongestCommonSubstring(); 
  55.         String result = obj.lcs(str1, str2);
  56.  
  57.         System.out.println("\nLongest Common Substring : "+ result);
  58.     }
  59. }

Longest Common Substring Algorithm Test
 
 
Enter string 1
abcdefghijklmnopqrstuvwxyz
 
Enter string 2
randomijklmnstring
 
Longest Common Substring : ijklmn

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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