Question

My code at the moment:

import java.util.*;
import java.io.*;

public class Percolation {
    // given an N-by-N matrix of open sites, return an N-by-N matrix
    // of sites reachable from the top via a vertical path of open sites
    private static Scanner scan = null;

    public static boolean[][] readOpenFromFile() {
        final File f = new File("file.txt");
        try {
            scan = new Scanner(f);
        }
        catch(FileNotFoundException ex) {
            System.exit(0);
        }

        final int m = scan.nextInt();
        final int n = scan.nextInt();
        final boolean[][] grid = new boolean[m][n];

        for(int i = 0; i < m; i++) {
            for(int j = 0; j < n; j++) {
                grid[i][j] = readBoolean();
            }
        }
        return grid;
    }

    public static boolean readBoolean() {
        final String s = scan.next();

        if(s.equalsIgnoreCase("true")) {
            return true;
        }
        if(s.equalsIgnoreCase("false")) {
            return false;
        }
        if(s.equals("1")) {
            return true;
        }
        if(s.equals("0")) {
            return false;
        }
        throw new java.util.InputMismatchException();
    }

    public static boolean[][] flow(final boolean[][] open) {
        final int n = open.length;
        final boolean[][] full = new boolean[n][n];
        for(int j = 0; j < n; j++) {
            flow(open, full, 0, j);
        }
        return full;
    }

    public static void flow(final boolean[][] open, final boolean[][] full, final int i, final int j) {
        final int n = open.length;

        // base cases
        if(( i < 0) ||( i >= n)) {
            return; // invalid row
        }
        if(( j < 0) ||( j >= n)) {
            return; // invalid column
        }
        if(!open[i][j]) {
            return; // not an open site
        }
        if(full[i][j]) {
            return; // already marked as full
        }

        // mark i-j as full
        full[i][j] = true;

        flow(open, full, i + 1, j); // down
        flow(open, full, i, j + 1); // right
        flow(open, full, i, j - 1); // left
        flow(open, full, i - 1, j); // up
    }

    // does the system percolate?
    public static boolean percolates(final boolean[][] open) {
        final int n = open.length;
        final boolean[][] full = flow(open);
        for(int j = 0; j < n; j++) {
            if(full[n - 1][j]) {
                System.out.println("percolates");
                return true;
            }
        }
        System.out.println("does not percolate");
        return false;
    }

    public static void print(final boolean[][] grid) {
        final int m = grid.length;
        final int n = grid[0].length;
        System.out.println(m + " " + n);
        for(int i = 0; i < m; i++) {
            for(int j = 0; j < n; j++) {
                if(grid[i][j]) {
                    System.out.print("1 ");
                } else {
                    System.out.print("0 ");
                }
            }
            System.out.println("");
        }
    }

    public static void main(String[] args) {
        final boolean[][] open = readOpenFromFile();
        print(flow(open));
        System.out.println(percolates(open));
    }
}

It can be seen that this program works by grabbing input from the file.txt file. However, how could I modify this code so as to request require a file name (perhaps at the command-line) each time the program is run, and use that as input?
I would think to add a String as an argument, then change that String into a file name. But this is easier said than done. Suggestions?

Answer 1

You can take it as an argument and modify code to –

public static void main(String[] args) {
    // args[0] - Full path of the file
    final boolean[][] open = readOpenFromFile(args[0]);
    print(flow(open));
    System.out.println(percolates(open));
}

public static boolean[][] readOpenFromFile(String filepath) {
    final File f = new File(filepath);
    try {
        scan = new Scanner(f);
    }
    catch(FileNotFoundException ex) {
        System.exit(0);
    }

    final int m = scan.nextInt();
    final int n = scan.nextInt();
    final boolean[][] grid = new boolean[m][n];

    for(int i = 0; i < m; i++) {
        for(int j = 0; j < n; j++) {
            grid[i][j] = readBoolean();
        }
    }
    return grid;
}