Rabin_Karp_Algo_Rolling_Hash

/* Following program is a C++ implementation of Rabin Karp 
Algorithm given in the CLRS book */
#include <bits/stdc++.h> 
using namespace std; 

// d is the number of characters in the input alphabet 
#define d 256 

/* pat -> pattern 
	txt -> text 
	q -> A prime number 
*/
void search(char pat[], char txt[], int q) 
{ 
	int M = strlen(pat); 
	int N = strlen(txt); 
	int i, j; 
	int p = 0; // hash value for pattern 
	int t = 0; // hash value for txt 
	int h = 1; 

	// The value of h would be "pow(d, M-1)%q" 
	for (i = 0; i < M - 1; i++) 
		h = (h * d) % q; 

	// Calculate the hash value of pattern and first 
	// window of text 
	for (i = 0; i < M; i++) 
	{ 
		p = (d * p + pat[i]) % q; 
		t = (d * t + txt[i]) % q; 
	} 

	// Slide the pattern over text one by one 
	for (i = 0; i <= N - M; i++) 
	{ 

		// Check the hash values of current window of text 
		// and pattern. If the hash values match then only 
		// check for characters on by one 
		if ( p == t ) 
		{ 
			/* Check for characters one by one */
			for (j = 0; j < M; j++) 
			{ 
				if (txt[i+j] != pat[j]) 
					break; 
			} 

			// if p == t and pat[0...M-1] = txt[i, i+1, ...i+M-1] 
			if (j == M) 
				cout<<"Pattern found at index "<< i<<endl; 
		} 

		// Calculate hash value for next window of text: Remove 
		// leading digit, add trailing digit 
		if ( i < N-M ) 
		{ 
			t = (d*(t - txt[i]*h) + txt[i+M])%q; 

			// We might get negative value of t, converting it 
			// to positive 
			if (t < 0) 
			t = (t + q); 
		} 
	} 
} 

/* Driver code */
int main() 
{ 
	char txt[] = "GEEKS FOR GEEKS"; 
	char pat[] = "GEEK"; 
	int q = 101; // A prime number 
	search(pat, txt, q); 
	return 0; 
} 

// This is code is contributed by rathbhupendra 

import java.nio.file.Path;
import java.util.*;

public class Solution
{

  private static final int d = 26; // Base value of alphabets
  private static final int p = 5381; // Large prime number

  public static void search(String pat, String txt)
  {
    int patHash = 0; // Hash value of pattern
    int txtHash = 0; // Hash value of text

    for (int i = 0; i < pat.length(); i++) // Generating Hash values for pattern and first window text
    {
      patHash = patHash * d;
      txtHash = txtHash * d;
      patHash = patHash + ((pat.charAt(i) - 'A' + 1) % p);
      txtHash = txtHash + ((txt.charAt(i) - 'A' + 1) % p);
    }

    
    for (int i = 0; i < txt.length() - pat.length(); i++) // Loop of text size minus  window
    {
      if (patHash == txtHash)
      {
        System.out.println("Pattern found at index " + i);
      }

      if (i < txt.length() - pat.length())
      {
        txtHash = txtHash - ((txt.charAt(i) - 'A' + 1) * (int)Math.pow(d, pat.length() - 1));  // Subtracting first element from current hash of d^window-1
        txtHash = txtHash * d + (txt.charAt(i + pat.length()) - 'A' + 1);  // multiplying obtained hash with d to left shift the number and then adding the next new element
      }
    }
  }
    
  public static void main(String []args)
  {
    String txt = "GEEKS FOR GEEKS";
    String pat = "GEEK";

    search(pat, txt);
  }  
}

You should change the loop condition to i <= txt.length() - pat.length() instead of i < txt.length() - pat.length(); the( <= )

package gfg;

import java.util.ArrayList;
import java.util.List;

public class RabinKarpRollHash
{
	 private static final int d = 26; // Base value of alphabets
	 private static final int p = 5381; // Large prime number
	
	private List<Integer> rollHash(String pattern, String text)
	{
		List<Integer> indices = new ArrayList<Integer>();
		int patHash = 0;
		int txtHash = 0;
		
		for (int i = 0,pow = pattern.length() - 1; i < pattern.length(); i++) // Generating Hash values for pattern and first window text
	    {
			patHash += (pattern.charAt(i) - 'A' + 1) * (int)Math.pow(d, pow);
			patHash %= p;
			txtHash += (text.charAt(i) - 'A' + 1) * (int)Math.pow(d, pow--);
			txtHash %= p;
	    }

		for (int i = 0; i <= text.length() - pattern.length(); i++)
		{
			//declaration
			String textToCompare = text.substring(i, i + pattern.length());
			int pow = pattern.length() - 1;
			
			//condition for matched pattern
			if (patHash == txtHash && match(textToCompare, pattern))
			{
				indices.add(i + 1);
			}
			
			//calculate hash till last pattern string
			if(i < text.length() - pattern.length())
			{
				//subtract
				txtHash = txtHash - (((text.charAt(i) - 'A' + 1) * (int)Math.pow(d, pow)) % p);
				//add
				txtHash = ((txtHash * d) + (text.charAt(i + pattern.length()) - 'A' + 1)) % p;
			}
			
			//negative hash value
			if (txtHash < 0)
			{
                             txtHash += p;
                         }
			
		}
		return indices;
	}
	
	private boolean match(String text, String pattern)
	{	
		boolean flag = true;
		for (int i = 0; i < pattern.length(); i++)
		{
			if(text.charAt(i) != pattern.charAt(i))
			{
				flag = false;
				break;
			}
		}
		
		return flag;
	}

	public static void main(String[] args)
	{
		RabinKarpRollHash soln = new RabinKarpRollHash();
		List<Integer> ans = soln.rollHash("ecda", "ecdadecdacde");
		System.out.println(ans);
	}
}

This is the code that i wrote to my understanding level, any corrections are welcomed

package gfg;

import java.util.ArrayList;

public class RabinKarpRollHash
{
	
	private ArrayList<Integer> rollHash(String pattern, String text)
	{
		ArrayList<Integer> indices = new ArrayList<Integer>();
		int patHash = 0;
		int txtHash = 0;
		
		for (char c : pattern.toCharArray())
		{
			patHash += c;
		}
		
		for (int i = 0; i < pattern.length(); i++)
		{
			txtHash += text.charAt(i);
		}

		for (int i = 0; i <= text.length() - pattern.length(); i++)
		{
			//declaration
			String textToCompare = text.substring(i, i + pattern.length());
			
			//condition for matched pattern
			if (patHash == txtHash && textToCompare.equals(pattern))
			{
				indices.add(i + 1);			
			}
			
			//calculate hash till last pattern string
			if(i < text.length() - pattern.length())
			{
				txtHash = txtHash - text.charAt(i) + text.charAt(i + pattern.length());
			}
			
		}
		return indices;
	}		

	public static void main(String[] args)
	{
		RabinKarpRollHash soln = new RabinKarpRollHash();
		ArrayList<Integer> ans = soln.rollHash("egibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebd", "egibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdibegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdcfegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdiiedegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdeghegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebddgddfegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdaedggagegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdadeaaheabidegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdbbegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdhaegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebddegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdeaaeaegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdhegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdiacegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdhegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebddegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdcegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdaihhccegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdfegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdiegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdaegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdccaegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdbegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdhicgggiegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdiagegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdabfgdfhbhegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdedegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdheaegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdgegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdgdcegibbbdbgdiedabcbidgdiicahagehfihbiedaebchicaaiebhibhcaihbahfedaadacegggcchihgbfgccficffdgaeiebdaadb");
		System.out.print(ans);
	}
}

I tried this without hash

import java.util.ArrayList;
import java.util.Scanner;

public class rabinKarp {
public static void main(String args[]) {
Scanner sc = new Scanner(System.in);
System.out.print("Enter the string1:- ");
String str1 = sc.nextLine();
System.out.print("Enter the string2:- ");
String str2 = sc.nextLine();
sc.close();
if (str2.length() > str1.length()) {
return;
}
rabin(str1, str2);
}

private static final int BASE = 256;
private static final long PRIME = 10000007;

private static void rabin(String txt, String pat) {
    // Precomputing BASE^(M-1) When Deleting the First Character It is useful
    long h = 1;
    for (int i = 0; i < pat.length() - 1; i++) {
        h = (h * BASE) % PRIME;
    }

    ArrayList<Integer> indexes = new ArrayList<>();

    long patHash = calculateHash(pat);
    long windowHash = calculateHash(txt.substring(0, pat.length()));

    for (int i = 0; i <= txt.length() - pat.length(); i++) {
        
        if (windowHash == patHash) {
            indexes.add(i);
        }
        
        System.out.println(patHash + " " + windowHash);
        int ascciOld = txt.charAt(i);

        // Remove first character from hash
       // ( windowHash - (1 * h) % prime + prime ) prime
        windowHash = (windowHash - (ascciOld * h) % PRIME + PRIME) % PRIME;

        if (i + pat.length() < txt.length()) {
            int ascciNew = txt.charAt(i + pat.length());
            // (windowHash * Base + assciNew) % prime
            windowHash = (windowHash * BASE + ascciNew) % PRIME;
        }

    }

    System.out.println(indexes);
}

private static long calculateHash(String str) {
    long hash = 0;
    for (int i = 0; i < str.length(); i++) {
        hash = (hash * BASE + str.charAt(i)) % PRIME;
    }
    return hash;
}

}