Flipping the Matrix HackerRank Solution in Java with Explanation

Java Solution for Flipping the Matrix | Find Highest Sum of Upper-Left Quadrant of Matrix

Problem Description :

Sean invented a game involving a 2n * 2n matrix where each cell of the matrix contains an integer. He can reverse any of its rows or columns any number of times. The goal of the game is to maximize the sum of the elements in the n *n submatrix located in the upper-left quadrant of the matrix.

Given the initial configurations for q matrices, help Sean reverse the rows and columns of each matrix in the best possible way so that the sum of the elements in the matrix's upper-left quadrant is maximal. 

Input :

matrix = [[1, 2], [3, 4]]

Output :

4

Input :

matrix = [[112, 42, 83, 119], [56, 125, 56, 49], [15, 78, 101, 43], [62, 98, 114, 108]]

Output :

119 + 114 + 56 + 125 = 414

Full Problem Description :

• Flipping the Matrix Problem Description 
  

Here we can find solution using following pattern,

So simply we have to find Max of same number of box like (1,1,1,1). And last return Sum of all Max numbers.

We have to return Sum of Top-Left Matrix (1, 2, 3, 4), But before that we have to find Max number from Matrix.

Solution 1 : Flipping the Matrix Solution in Java

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;

class Result {

    public static int flippingMatrix(List<List<Integer>> matrix) {
        int sum = 0;
        int size = matrix.size();
        for (int i = 0; i < size/2; i++) {
            for (int j = 0; j < size/2; j++) {
                sum += Math.max( matrix.get(i).get(j),
                    Math.max( matrix.get(i).get(size-1-j),
                    Math.max( matrix.get(size-1-i).get(j),
                        matrix.get(size-1-i).get(size-1-j))
                    ) 
                );
            }           
        }
        return sum;
    }
}

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

        int q = Integer.parseInt(bufferedReader.readLine().trim());

        IntStream.range(0, q).forEach(qItr -> {
            try {
                int n = Integer.parseInt(bufferedReader.readLine().trim());

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

                IntStream.range(0, 2 * n).forEach(i -> {
                    try {
                        matrix.add(
                            Stream.of(bufferedReader.readLine().replaceAll("\\s+$", "").split(" "))
                                .map(Integer::parseInt)
                                .collect(toList())
                        );
                    } catch (IOException ex) {
                        throw new RuntimeException(ex);
                    }
                });

                int result = Result.flippingMatrix(matrix);

                bufferedWriter.write(String.valueOf(result));
                bufferedWriter.newLine();
            } catch (IOException ex) {
                throw new RuntimeException(ex);
            }
        });

        bufferedReader.close();
        bufferedWriter.close();
    }
}

Solution Explanation :

matrix = [[112, 42, 83, 119], [56, 125, 56, 49], [15, 78, 101, 43], [62, 98, 114, 108]]

We have to return Sum of all Max numbers that have same colors. like first we have to find Max from [112, 119, 62, 108] and so on.

• We are looping through only half of list because we have to find Sum of Top-Left corner of matrix.
• As traverse through given List of List we are getting following answer in sum variable.
1. sum += Max [112, 119, 62, 108] | sum = 0 + 119
2. sum += Max [42, 83, 98, 114] | sum = 119 + 114 = 233
3. sum += Max [56, 49, 15, 43] | sum = 233 + 56 = 289
4. sum += Max [125, 56, 78, 101] | sum = 289 + 125 = 414
• return sum

 

Happy learning... Happy coding...

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