tetris

Tetris is widely known as one of the most popular computer puzzle games of all time. A random sequence of tetrominoes (sometimes called "tetrads" in older versions) - shapes composed of four square blocks each - fall down the playing field. The object of the game is to manipulate these tetrominoes with the aim of creating a horizontal line of blocks without gaps. When such a line is created, it disappears, and the blocks above (if any) fall. As the game progresses, the tetrominoes fall faster, and the game ends when the player "tops out", that is, when the stack of tetrominoes reaches the top of the playing field and no new tetrominoes are able to enter.

The seven one-sided tetrominoes in Tetris are referred to as I, J, L, O, S, T, and Z. All are capable of single and double clears. I, J, and L are able to clear triples. Only the I tetromino has the capacity to clear four lines simultaneously, and this clear is referred to as a "tetris." (This may vary depending on the rotation and compensation rules of each specific Tetris implementation. For instance, in the Tetris Worlds type rules (see below) used in many recent implementations, certain rare situations allow T, S and Z to 'snap' into tight spots, clearing triples.)

The seven possible Tetris pieces in their Tetris Worlds colors. Top row: I, J, L, O. Bottom row: S, T, Z.

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