Swapping 2D matrix diagonal with a middle line

Question

I have a Java 2D array

String arraylist numberSeq[][];

inside the array list, there is number from 1 to 25,

numberSeq[0][0] = 1, [0][1] = 2, [0][2] = 3 , [0][3] = 4 , [0][4] = 5
numberSeq[1][0] = 6, [1][1] = 7, [1][2] = 8 , [1][3] = 9 , [1][4] = 10
......
numberSeq[4][0] = 21,[4][1] = 22,[4][2] = 23, [4][3] = 24, [4][4] = 25

So the number will be like

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

After doing a diagonals swap, I wish the output to be like

25 20 15 10 5
24 19 14 9  4
23 18 13 8  3
22 17 12 7  2
21 16 11 6  1

How can I achieve that when I can only declare one local variable?

If one local variable is not achievable, how much is the minimum number of local variables I need?

Answer 1

You can do this by making another teo dimensional array, iterating through your first in the right order and post it to a new one.

public class MyClass {
    public static void main(String args[]) {

        int dimension = 5;

        int[][] numberSeq = new int[dimension][dimension];

        numberSeq[0][0] = 1; numberSeq[0][1] = 2;numberSeq[0][2] = 3;numberSeq[0][3] = 4;numberSeq[0][4] = 5;
        numberSeq[1][0] = 6; numberSeq[1][1] = 7;numberSeq[1][2] = 8;numberSeq[1][3] = 9;numberSeq[1][4] = 10;
        numberSeq[2][0] = 11;numberSeq[2][1] = 12;numberSeq[2][2] = 13;numberSeq[2][3] = 14;numberSeq[2][4] = 15;
        numberSeq[3][0] = 16;numberSeq[3][1] = 17;numberSeq[3][2] = 18;numberSeq[3][3] = 19;numberSeq[3][4] = 20;
        numberSeq[4][0] = 21;numberSeq[4][1] = 22;numberSeq[4][2] = 23;numberSeq[4][3] = 24;numberSeq[4][4] = 25;

        int[][] flippedSeq = new int[dimension][dimension];

        // This is the flipping part
        for(int i = 0; i < dimension; i++)
        {
            for(int j = 0; j < dimension; j++)
            {
                flippedSeq[i][j] = numberSeq[dimension-1-j][dimension-1-i];
            }
        }

        PrintMatrix(numberSeq);
        System.out.println();
        PrintMatrix(flippedSeq);


    }

    public static void PrintMatrix(int[][] mat)
    {
        for(int i = 0; i < mat.length; i++)
        {
            for(int j = 0; j < mat[i].length; j++)
                System.out.print(mat[i][j] + " ");
            System.out.println();
        }
    }
}

I hope thats what you meant by "1 local variable".

Output is:

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 

25 20 15 10 5 
24 19 14 9 4 
23 18 13 8 3 
22 17 12 7 2 
21 16 11 6 1