Diagonal Difference – Java HackerRank Solution

Objective:

This diagonal difference problem involves basic matrix traversal and arithmetic operations to calculate the required difference. Calculate the absolute difference between the sums of the matrix’s two diagonals.

Problem Statement:

You are given a square matrix of integers. Your task is to calculate the absolute difference between the sums of its primary (top-left to bottom-right) and secondary (top-right to bottom-left) diagonals.

Input Format:

• The first line contains a single integer n, the number of rows and columns in the matrix.
• Each of the next n lines contain n space-separated integers representing the elements of the matrix.

Output Format:

• A single integer represents the absolute difference between the sums of the primary and secondary diagonals.

Example 1:

1. Input:
   • n = 3
   • matrix =
1 2 4
4 5 6
10 8 -12
2. Output:
   • 15
   • Explanation: The primary diagonal is 11, 5, -12, and the secondary diagonal is 4, 5, 10.
     • Primary diagonal sum: 11 + 5 – 12 = 4
     • Secondary diagonal sum: 4 + 5 + 10 = 19
     • Absolute difference: |4 – 19| = 15

Example 2:

1. Input:
   • n = 2
   • matrix =
1 2
3 4
2. Output:
   • 0
   • Explanation: The primary diagonal is 1, 4, and the secondary diagonal is 2, 3.
     • Primary diagonal sum: 1 + 4 = 5
     • Secondary diagonal sum: 2 + 3 = 5
     • Absolute difference: |5 – 5| = 0

Example 3:

1. Input:
   • n = 4
   • matrix =
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16
2. Output:
   • 0
   • Explanation: The primary diagonal is 1, 6, 11, 16, and the secondary diagonal is 4, 7, 10, 13.
     • Primary diagonal sum: 1 + 6 + 11 + 16 = 34
     • Secondary diagonal sum: 4 + 7 + 10 + 13 = 34
     • Absolute difference: |34 – 34| = 0

Steps to Solve:

1. Initialize Sums: Start with sums for the primary and secondary diagonals set to 0.
2. Traverse the Matrix: Loop through the matrix to add up the elements of the primary and secondary diagonals.
   • The primary diagonal elements are at the indices (i, i).
   • The secondary diagonal elements are at the indices (i, n-1-i).
3. Calculate Absolute Difference: Compute the absolute difference between the two sums.
4. Output the Result: Print the absolute difference.

Diagonal Difference Problem Snippet:

Diagonal Difference Solution:

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 {

    /*
     * Complete the 'diagonalDifference' function below.
     *
     * The function is should return an INTEGER.
     * The function accepts 2D_INTEGER_ARRAY arr as parameter.
     */

    public static int diagonalDifference(List<List<Integer>> arr) {
        // Write your code here
        int diagonal1 = 0;
        int diagonal2 = 0;
        int length = arr.get(0).size() - 1;
        for(int i=0; i<= length; i++){
            diagonal1 += arr.get(i).get(i);
            diagonal2 += arr.get(i).get(length-i);
        }
        return Math.abs(diagonal1 - diagonal2);
    }

}

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 n = Integer.parseInt(bufferedReader.readLine().trim());

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

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

        int result = Result.diagonalDifference(arr);

        bufferedWriter.write(String.valueOf(result));
        bufferedWriter.newLine();

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

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