Accessing elements of multi-dimensional Lists in Java

Question

There was this problem on HackerRank Day 11: 2D Arrays[1](Read the problem statement here) in which can be solved easily using arrays. But they have used 2D lists to store the data. But i could'nt figure out anyways to access contents of multi-dimensional lists by refering their index.

This is the code given to solve:

import java.io.*;
import java.math.*;
import java.security.*;
import java.text.*;
import java.util.*;
import java.util.concurrent.*;
import java.util.function.*;
import java.util.regex.*;
import java.util.stream.*;
import static java.util.stream.Collectors.joining;
import static java.util.stream.Collectors.toList;

public class Solution {
    public static void main(String[] args) throws IOException {
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));

        List<List<Integer>> arr = new ArrayList<>();

        IntStream.range(0, 6).forEach(i -> {
            try {
                arr.add(
                    Stream.of(bufferedReader.readLine().replaceAll("\\s+$", "").split(" "))
                        .map(Integer::parseInt)
                        .collect(toList())
                );
            } catch (IOException ex) {
                throw new RuntimeException(ex);
            }
        });

        bufferedReader.close();
    }
}

What are the possible solutions for this problem using Lists.

I tried by using toArray() method and get() method in various ways but failed. Any help would be appreciated. [1]: https://www.hackerrank.com/challenges/30-2d-arrays/problem

Answer 1

int maxval = -6*9;
for(int i = 0; i < 4; i++) {
    for(int j = 0; j < 4; j++) {
        //System.out.print(arr.get(i).get(j) + " ");
        int sum = arr.get(i).get(j) + arr.get(i).get(j+1) + arr.get(i).get(j+2);
        sum+=arr.get(i+1).get(j+1);
        sum+=arr.get(i+2).get(j) + arr.get(i+2).get(j+1) + arr.get(i+2).get(j+2);
        if(sum > maxval)   
            maxval = sum;
        }
    }
    System.out.println(maxval);