Today I was training algorithms and data structures on hackerrank.com. Here is one example:

Given a square matrix of size NxN, calculate the absolute difference between the sums of its diagonals.

import java.util.Scanner;

public class DiagonalAbsoluteSum {

 static int sumA = 0;
 static int sumB = 0;

 public static void main(String[] args) {
  Scanner in = new Scanner(System.in);
  int n = in.nextInt();
  int a[][] = new int[n][n];
  for (int a_i = 0; a_i < n; a_i++) {
   for (int a_j = 0; a_j < n; a_j++) {
    a[a_i][a_j] = in.nextInt();
   }
  }

  for (int i = 0; i < a.length; i++) {
   sumA += a[i][i];
  }

  for (int i = 0; i < a.length; i++) {

   sumB += a[i][a.length - i - 1];
  }

  System.out.println(Math.abs(sumA - sumB));
 }

}