DiagonalSum.java

public class DiagonalSum {
    public static int DSum(int matrix[][]) {
        int sum = 0;
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix[0].length; j++) {
                if (i == j) {
                    sum += matrix[i][j];
                } else if (i + j == matrix.length - 1) {
                    sum += matrix[i][j];
                }
            }
        }
        return sum;
    }

    public static int OptimisedDsum(int[][] matrix) {
        int sum = 0;
        for (int i = 0; i < matrix.length; i++) {
            sum += matrix[i][i];

            if (i != matrix.length - 1-i) {
                sum += matrix[i][matrix.length - 1 - i];
            }
        }

        return sum;

    }

    public static void main(String[] args) {
        int matrix[][] = { { 1, 2, 3, 4, 5 },
                { 6, 7, 8, 9, 10 },
                { 11, 12, 13, 14, 15 },
                { 16, 17, 18, 19, 20 },
                { 21, 22, 23, 24, 25 } };

        System.out.println(DSum(matrix));
        System.out.println(OptimisedDsum(matrix));
    }

}