Longest Common Substring

The longest common substring problem can be easily solved using a matrix approach.
A simple google search will show the process.

Here is a working C++ code of the same:

/*

 Copyright: Puneet Sohi 

 */

#include <iostream>

#include <string>

#include <vector>

#include <tr1/unordered_map>

using namespace std;

using namespace tr1;

void findLongestCommonSubstring(string s1, string s2){

if (s1.size() == 0 || s2.size() == 0){

cout << "input NULL, no common substring!"<< endl;

}

int i = 0;

int j = 0;

int a[100][100];

//int a[s1.size()+1][s2.size()+1];

string l_substr;

int l_count=0;

int temp;

while(i<s1.size()){

//cout << "entry1" << endl;

        j=0;

while(j<s2.size()){

//cout << "entry2" << endl;

//cout << "i: " << i << "j: " << j << endl;

if(s1[i] == s2[j]){

cout << "match at i: "<< i << " j: " << j << endl;

//cout << "a[i][j] = "<< a[i][j] << endl;

a[i+1][j+1] = a[i][j]+1;

//cout << "a[i+1][j+1]"<< a[i+1][j+1] << endl;

temp = a[i+1][j+1];

cout << "temp: " << temp << endl;

if(temp > l_count){

//new longest count found

l_count = temp;

l_substr = s1.substr(i-temp+1, temp);

cout << "new longest substr found, " << "lcount: " << l_count << endl;

cout << "Substr: " << l_substr << endl;

}

}

j++;

}

i++;

}

cout << "length of longest common substring: " << l_count << endl;

cout << "longenst common substring is: "<< l_substr << endl;

return;

}

int main () {

string s1 = "adfdfdsfahardyadffadsf";

string s2 = "hardyplokmijn";  //o/p shud be hardyharhar

findLongestCommonSubstring(s1, s2);

    return 0;

}