Rotating blocks in 2D-array

Question

I am making a program similar to the famous game Tetris and I've run into some problems when it comes to rotating a block.

I know you are able to rotate figures in a coordinate system by using "x = -y" and "y = x" but the problem is that because I am using an array of integers to represent the block it makes things so much more difficult.

My array looks like:

int[][] space = new int[20][10];

And if a coordinate contains a block the value is 1 else it's 0.

So how can I rotate a block in that space without getting trouble with negative numbers?

Answer 1

Here's a sample piece (reusing your int[][] using 0's and 1's, which might as well be done using a boolean array):

private static final int[][] piece = new int[][] {
        { 0, 1, 0, },
        { 1, 1, 1, },
};

You can rotate a piece doing this:

private static int[][] rotate( final int[][] piece ) {
    final int[][] res = new int[piece[0].length][piece.length];
    for (int x = 0; x < piece.length; x++) {
        for (int y = 0; y < piece[0].length; y++) {
            res[(res.length-1)-y][x] = piece[x][y];
        }
    }
    return res;
}

The starting piece:

010
111

Here's rotate(piece):

01
11
01

Here's rotate(rotate(piece)):

111
010

And here's rotate(rotate(rotate(piece))):

10
11
10