We consider the problem of coloring a grid using k colors with the restriction that in each row and each column has an specific number of cells of each color. In an already classical result, Ryser obtained a necessary and sufficient condition for the existence of such a coloring when two colors are considered. This characterization yields a linear time algorithm for constructing such a coloring when it exists. Gardner et al. showed that for k≥7 the problem is NP-hard. Afterward Chrobak and Dürr improved this result, by proving that it remains NP-hard for k≥4. We solve the gap by showing that for 3 colors the problem is already NP-hard. Besides we also give some results on tiling tomography. © 2009 Springer Berlin Heidelberg.
CITATION STYLE
Dürr, C., Guiñez, F., & Matamala, M. (2009). Reconstructing 3-colored grids from horizontal and vertical projections is np-hard. In Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) (Vol. 5757 LNCS, pp. 776–787). https://doi.org/10.1007/978-3-642-04128-0_69
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