We analyze the problem of packing squares in an online fashion: Given a semi-infinite strip of width 1 and an unknown sequence of squares of side length in [0,1] that arrive from above, one at a time. The objective is to pack these items as they arrive, minimizing the resulting height. Just like in the classical game of Tetris, each square must be moved along a collision-free path to its final destination. In addition, we account for gravity in both motion (squares must never move up) and position (any final destination must be supported from below). A similar problem has been considered before; the best previous result is by Azar and Epstein, who gave a 4-competitive algorithm in a setting without gravity (i.e., with the possibility of letting squares "hang in the air") based on ideas of shelf-packing: Squares are assigned to different horizontal levels, allowing an analysis that is reminiscent of some bin-packing arguments. We apply a geometric analysis to establish a competitive factor of 3.5 for the bottom-left heuristic and present a 34 13=2.615...-competitive algorithm.
strip packing problem!Tetris and gravity constraint There is one negative result for the setting with Tetris and gravity constraint when rotation is not allowed in @cite_12 : If all rectangles have a width of at least @math or of at most @math , then the competitive factor of any algorithms is @math .
@cite_12
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The paper considerspacking of rectanglesinto an infinite bin. Similar to theTetris game, the rectangles arrive from the top and, once placed, cannot be moved again. The rectangles are moved inside the bin to reach their place. For the case in which rotations are allowed, we design an algorithm whose performance ratio is constant. In contrast, if rotations are not allowed, we show that no algorithm of constant ratio exists. For this case we design an algorithm with performance ratio ofO(log(1 ?)), where ? is the minimum width of any rectangle. We also show that no algorithm can achieve a better ratio than?(log(1 ?))for this case.