Java Program to Implement the String Search Algorithm for Short Text Sizes

// Java Program to Implement the String Search
// Algorithm for Short Text Sizes

import java.io.*;

class GFG {
    public static void main(String[] args)
    {

        String text = "geeksforgeeks is a coding website for geeks";
        String pattern = "geeks";

        // calling the method that is designed for
        // printing the instances of pattern
        // found in the text string
        stringMatch(text, pattern);
    }
    public static void stringMatch(String text, String pattern)
    {

        int len_t = text.length();
        int len_p = pattern.length();

        int k = 0, i = 0, j = 0;

        // loop to find out the position Of searched pattern
        for (i = 0; i <= (len_t - len_p); i++) {

            for (j = 0; j < len_p; j++)
            {
                if (text.charAt(i + j) != pattern.charAt(j))
                    break;
            }
          
            if (j == len_p)
            {
                k++;
                System.out.println("Pattern Found at Position: " + i);
            }
        }
      
        if (k == 0)
            System.out.println("No Match Found!");
        else
            System.out.println("Total Instances Found = " + k);
    }
}

// Java Program to Implement the String Search
// Algorithm for Short Text Sizes

class KMP_String_Matching {
    void KMPSearch(String pat, String txt)
    {
        int M = pat.length();
        int N = txt.length();

        // create lps[] that will hold the longest
        // prefix suffix values for pattern
        int lps[] = new int[M];
        int j = 0; // index for pat[]

        // Preprocess the pattern (calculate lps[]
        // array)
        computeLPSArray(pat, M, lps);

        int i = 0; // index for txt[]
        while (i < N) {
            if (pat.charAt(j) == txt.charAt(i)) {
                j++;
                i++;
            }
            if (j == M) {
                System.out.println("Found pattern "
                                   + "at index " + (i - j));
                j = lps[j - 1];
            }

            // mismatch after j matches
            else if (i < N
                     && pat.charAt(j) != txt.charAt(i)) {
                // Do not match lps[0..lps[j-1]] characters,
                // they will match anyway
                if (j != 0)
                    j = lps[j - 1];
                else
                    i = i + 1;
            }
        }
    }

    void computeLPSArray(String pat, int M, int lps[])
    {
        // length of the previous longest prefix suffix
        int len = 0;
        int i = 1;
        lps[0] = 0; // lps[0] is always 0

        // the loop calculates lps[i] for i = 1 to M-1
        while (i < M) {
            if (pat.charAt(i) == pat.charAt(len)) {
                len++;
                lps[i] = len;
                i++;
            }
            else // (pat[i] != pat[len])
            {
                // This is tricky. Consider the example.
                // AAACAAAA and i = 7. The idea is similar
                // to search step.
                if (len != 0) {
                    len = lps[len - 1];

                    // Also, note that we do not increment
                    // i here
                }
                else // if (len == 0)
                {
                    lps[i] = len;
                    i++;
                }
            }
        }
    }

    // Driver program to test above function
    public static void main(String args[])
    {
        String text
            = "geeksforgeeks is a coding website for geeks";
        String pattern = "geeks";

        KMP_String_Matching effective
            = new KMP_String_Matching();
        effective.KMPSearch(pattern, text);
    }
}