从其他类调用静态方法时，如何更改对象的值？

Question

In this practice problem, a square matrix filled with 0s and 1s is instantiated. You can flip over values (ex: 0 becomes 1 and 1 becomes 0) in a rectangle of any size, as long as the topmost corner of the rectangle is [0, 0] in the matrix. The end goal is to find how many times you must flip values over to get all the values of the matrix as 0.

If you want a longer explanation, go to http://usaco.org/index.php?page=viewproblem2&cpid=689 , but that's the basic outline.

This is my code:

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

public class CowTip {

    static int[][] mat;

    public static void main( String[] args) throws IOException, InterruptedException{

        Scanner scan = new Scanner(new File("cowtip.in"));

        int n = scan.nextInt();
        scan.nextLine();

        mat = new int[n][n];

        for (int x = 0; x < n; x++) {
            String str = scan.nextLine();
            for (int y = 0; y < n; y++) {
                mat[x][y] = Integer.parseInt(str.substring(y,y+1));
            }
        }

        Checker c = new Checker(n-1, n-1);

        int count = 0;
        while (true) {
            c.check();

            for (int x = 0; x <= c.row; x++) {
                for (int y = 0; y <= c.col; y++) {
                    if (mat[x][y] == 0) {
                        mat[x][y] = 1;
                    }
                    else if (mat[x][y] == 1) {
                        mat[x][y] = 0;
                    }
                }
            }
            count++;

            c.check();

            if (c.row == -1 && c.col == -1) {
                break;
            }

        }

        System.out.println(count);

    }

    static class Checker {

        int row;
        int col;

        public Checker(int r, int c) {
            row = r;
            col = c;
        }

        public Checker check() {
            Checker check = new Checker(-1, -1);
            for (int x = mat.length-1; x >= 0; x--) {
                for (int y = mat[x].length-1; y >= 0; y--) {
                    if (mat[x][y] == 1) {
                        check = new Checker(x, y);
                        break;
                    }
                }
                if (check.row != -1 && check.col != -1) {
                    break;
                }
            }
            return check;
        }

    }

}

and this is the input file (named cowtip.in) :

3
001
111
111

I've excluded my current debugging code, but the problem is that the row and col values inside my check() method are the correct values, but whenever I call the check() method in my main , the values reverts back to the default and doesn't give me the correct answer, which in turn makes the loop infinite.

Any ideas on how to fix this?

EDIT: I've figured it out, but thanks guys! It was actually extremely simple ( c = c.ckeck() instead of c.check() ) and honestly, I was pretty frustrated considering I spent around two hours trying to debug this...

Answer 1

将c.check()替换为c = c.check();