Need Help With Input/Output

General Questions
#1

I’m trying Shell Game. Since it’s from before December 2020, it requires the input to be read from a file and outputted to a file. My question is about this, but I am providing more of the code to show how I used it. (This is in Java):

File inputFile = new File("shell.in");
Scanner reader = new Scanner(inputFile);
FileWriter writer = new FileWriter("shell.out");
int n = reader.nextInt();
for (int i = 0; i < n; i++) {
    for (int j = 0; j < 3; j++) {
        inputs[i][j] = reader.nextInt();
    }
}
...
writer.write(Math.max(Math.max(shell1, shell2), shell3));
writer.close();
reader.close();

I already tried the method on the usaco guide, and it did not work, so I tried this way. It doesn’t output anything to the file, so I wanted to know what I was doing wrong. Thank you in advance!

#2

Can you include all of your code (as mentioned in How to ask for help on a problem - #2)?

#3 
import java.io.File;
import java.util.Scanner;
import java.io.IOException;
import java.io.FileWriter;

class Main {
    public static void main(String[] args) throws IOException {
        File inputFile = new File("shell.in");
        Scanner reader = new Scanner(inputFile);
        FileWriter writer = new FileWriter("shell.out");
        int n = reader.nextInt();
        int[][] inputs = new int[n][3];
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < 3; j++) {
                inputs[i][j] = reader.nextInt();
            }
        }
        int[] shells = {1, 2, 3};
        int shell1 = 0;
        int shell2 = 0;
        int shell3 = 0;
        for (int k = 0; k < n; k++) {
            shells = swap(inputs[k][0] - 1, inputs[k][1] - 1, shells);
            int guess = inputs[k][2];
            if (shells[guess - 1] == 1) {
                shell1++;
            } else if (shells[guess - 1] == 2) {
                shell2++;
            } else {
                shell3++;
            }
        }
        writer.write(Math.max(Math.max(shell1, shell2), shell3));
        writer.close();
        reader.close();
    }

    public static int[] swap(int index1, int index2, int[] nums) {
        int temp = nums[index1];
        nums[index1] = nums[index2];
        nums[index2] = temp;
        return nums;
    }
}
#4

Switching to PrintWriter and using print instead of write works:

import java.io.File;
import java.util.Scanner;
import java.io.IOException;
import java.io.PrintWriter;

class Main {
    public static void main(String[] args) throws IOException {
        File inputFile = new File("shell.in");
        Scanner reader = new Scanner(inputFile);
        PrintWriter writer = new PrintWriter("shell.out");
        int n = reader.nextInt();
        int[][] inputs = new int[n][3];
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < 3; j++) {
                inputs[i][j] = reader.nextInt();
            }
        }
        int[] shells = {1, 2, 3};
        int shell1 = 0;
        int shell2 = 0;
        int shell3 = 0;
        for (int k = 0; k < n; k++) {
            shells = swap(inputs[k][0] - 1, inputs[k][1] - 1, shells);
            int guess = inputs[k][2];
            if (shells[guess - 1] == 1) {
                shell1++;
            } else if (shells[guess - 1] == 2) {
                shell2++;
            } else {
                shell3++;
            }
        }
        writer.print(Math.max(Math.max(shell1, shell2), shell3));
        writer.close();
        reader.close();
    }

    public static int[] swap(int index1, int index2, int[] nums) {
        int temp = nums[index1];
        nums[index1] = nums[index2];
        nums[index2] = temp;
        return nums;
    }
}

The method in USACO Guide is correct as far as I know (if not, let us know which specific part did not work).