PascalRecursive

import java.util.Scanner;

public class PascalRecursive {
    public static void main(String[] args) {
        try (Scanner scan = new Scanner(System.in)) {
            System.out.println("----- Welcome to Pascal Triangle (Recursive) -----");
            while (true) {
                int rows;
                while (true) {
                    System.out.println("\nEnter number of rows (positive integer) or 'bye' to quit:");
                    String input = scan.nextLine().trim();
                    if (input.matches("(?i).*(bye|exit|quit).*")) {
                        System.out.println("Goodbye!");
                        return;
                    }
                    if (input.matches("\\d+") && Integer.parseInt(input) > 0) {
                        rows = Integer.parseInt(input);
                        break;
                    } else {
                        System.out.println("Invalid input!");
                    }
                }

                long start = System.currentTimeMillis(); // Start timing before computation

                printPascalRecursive(rows); // Call recursive function

                long end = System.currentTimeMillis(); // End timing after computation

                System.out.println("Recursive method duration: " + (end - start) + " ms\n");

                while (true) {
                    System.out.println("\nPlay again? (y/n)");
                    String again = scan.nextLine().trim();
                    switch (again.toLowerCase()) {
                        case "n" -> {
                            System.out.println("Program ended. Goodbye!");
                            return;
                        }
                        case "y" -> {
                            break;
                        }
                        default -> {
                            System.out.println("Invalid input!");
                            continue;
                        }
                    }
                    break; // Exit loop and restart program
                }
            }
        }
    }

    // Recursive function to compute Pascal's Triangle values
    public static int pascal(int row, int column) {
        if (column == 0 || column == row)
            return 1;
        return pascal(row - 1, column - 1) + pascal(row - 1, column);
    }

    // Print Pascal's Triangle using recursive calculations
    public static void printPascalRecursive(int rows) {
        int maxWidth = 4 * rows; // Define maximum width for alignment
        for (int row = 0; row < rows; row++) {
            // Print leading spaces to center the row
            System.out.printf("%" + (maxWidth - 2 * row) + "s", "");
            for (int column = 0; column <= row; column++) {
                System.out.printf("%4d", pascal(row, column)); // Format numbers for alignment
            }
            System.out.println(); // Move to the next line
        }
    }
}