Print Longest Common Substring Using C++

In this tutorial, we will be discussing a program to print the longest common substring.

For this we will be given two strings say A and B. We have to print the longest substring common to the two input strings A and B.

For example, if we are given with “HelloWorld” and “world book”. Then the longest common substring, in this case, will be the “world”.

Example

#include <iostream>
#include <stdlib.h>
#include <string.h>
using namespace std;
void print_lstring(char* X, char* Y, int m, int n){
   int longest[m + 1][n + 1];
   int len = 0;
   int row, col;
   for (int i = 0; i <= m; i++) {
      for (int j = 0; j <= n; j++) {
         if (i == 0 || j == 0)
            longest[i][j] = 0;
         else if (X[i - 1] == Y[j - 1]) {
            longest[i][j] = longest[i - 1][j - 1] + 1;
            if (len < longest[i][j]) {
               len = longest[i][j];
               row = i;
               col = j;
            }
         }
         else
            longest[i][j] = 0;
         }
      }
      if (len == 0) {
         cout << "There exists no common substring";
      return;
   }
   char* final_str = (char*)malloc((len + 1) * sizeof(char));
   while (longest[row][col] != 0) {
      final_str[--len] = X[row - 1];
      row--;
      col--;
   }
   cout << final_str;
}
int main(){
   char X[] = "helloworld";
   char Y[] = "worldbook";
   int m = strlen(X);
   int n = strlen(Y);
   print_lstring(X, Y, m, n);
   return 0;
}

Output

world