import java.io.*;

import java.util.*;

​

public class PatternSearch {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

​

        System.out.println("How many lines you want to read from the text file?");

        int numLines = scanner.nextInt();

        scanner.nextLine(); // Consume newline

​

        System.out.println("How many patterns to be generated?");

        int numPatterns = scanner.nextInt();

        scanner.nextLine(); // Consume newline

​

        System.out.println("What is the length of each pattern?");

        int patternLength = scanner.nextInt();

        scanner.nextLine(); // Consume newline

​

        // Read text from input file

        StringBuilder textBuilder = new StringBuilder();

        try (BufferedReader br = new BufferedReader(new FileReader("input.txt"))) {

            String line;

            int linesRead = 0;

            while ((line = br.readLine()) != null && linesRead < numLines) {

                textBuilder.append(line.toLowerCase());

                textBuilder.append("\n");

                linesRead++;

            }

        } catch (IOException e) {

            e.printStackTrace();

            return;

        }

        String text = textBuilder.toString();

​

        // Generate random patterns

        List<String> patterns = generateRandomPatterns(text, numPatterns, patternLength);

​

        // Write patterns to file

        try (PrintWriter writer = new PrintWriter("patterns.txt")) {

            for (String pattern : patterns) {

                writer.println(pattern);

            }

        } catch (IOException e) {

            e.printStackTrace();

            return;

        }

​

        // Create shift tables and display them

        List<Map<Character, Integer>> shiftTables = createShiftTables(patterns);

        for (int i = 0; i < patterns.size(); i++) {

            System.out.println("Shift table for pattern " + (i + 1) + ": " + shiftTables.get(i));

        }

​

        // Brute force search

        long startTimeBF = System.nanoTime();

        for (String pattern : patterns) {

            bruteForceSearch(text, pattern);

        }

        long endTimeBF = System.nanoTime();

        long durationBF = (endTimeBF - startTimeBF) / numPatterns;

​

        // Horspool search

        long startTimeHorspool = System.nanoTime();

        for (String pattern : patterns) {

            horspoolSearch(text, pattern, shiftTables.get(patterns.indexOf(pattern)));

        }

        long endTimeHorspool = System.nanoTime();

        long durationHorspool = (endTimeHorspool - startTimeHorspool) / numPatterns;

​

        System.out.println("Average running time of Brute Force: " + durationBF + " nanoseconds");

        System.out.println("Average running time of Horspool: " + durationHorspool + " nanoseconds");

    }

​

    private static List<String> generateRandomPatterns(String text, int numPatterns, int patternLength) {

        List<String> patterns = new ArrayList<>();

        Random random = new Random();

        int maxStartIndex = text.length() - patternLength;

        for (int i = 0; i < numPatterns; i++) {

            int startIndex = random.nextInt(maxStartIndex);

            String pattern = text.substring(startIndex, startIndex + patternLength);

            patterns.add(pattern);

        }

        return patterns;

    }

​

    private static List<Map<Character, Integer>> createShiftTables(List<String> patterns) {

        List<Map<Character, Integer>> shiftTables = new ArrayList<>();

        for (String pattern : patterns) {

            Map<Character, Integer> shiftTable = new HashMap<>();

            for (int i = 0; i < pattern.length() - 1; i++) {

                shiftTable.put(pattern.charAt(i), pattern.length() - 1 - i);

            }

            shiftTables.add(shiftTable);

        }

        return shiftTables;

    }

​

    private static void bruteForceSearch(String text, String pattern) {

        int n = text.length();

        int m = pattern.length();

        for (int i = 0; i <= n - m; i++) {

            int j;

            for (j = 0; j < m; j++) {

                if (text.charAt(i + j) != pattern.charAt(j)) {

                    break;

                }

            }

            if (j == m) {

                // Pattern found at index i

            }

        }

    }

​

    private static void horspoolSearch(String text, String pattern, Map<Character, Integer> shiftTable) {

        int n = text.length();

        int m = pattern.length();

        int i = 0;

        while (i <= n - m) {

            int j = m - 1;

            while (j >= 0 && pattern.charAt(j) == text.charAt(i + j)) {

                j--;

            }

            if (j < 0) {

                // Pattern found at index i

                i += shiftTable.getOrDefault(text.charAt(i + m - 1), m);

            } else {

                i += shiftTable.getOrDefault(text.charAt(i + j), m);

            }

        }

    }

}