# Reconstructing 3-Colored Grids from Horizontal and Vertical Projections is NP-Hard: A Solution to the 2-Atom Problem in Discrete Tomography

1 RO - Recherche Opérationnelle
LIP6 - Laboratoire d'Informatique de Paris 6
Abstract : We consider the problem of coloring a grid using k colors with the restriction that each row and each column has a specific number of cells of each color. This problem has been known as the $(k-1)$-atom problem in the discrete tomography community. 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 $k\geqslant 7$ the problem is NP-hard. Afterward Chrobak and Dürr improved this result by proving that it remains NP-hard for $k\geqslant 4$. We close the gap by showing that for $k=3$ colors the problem is already NP-hard. In addition, we give some results on tiling tomography problems.
Document type :
Journal articles
Domain :

https://hal.archives-ouvertes.fr/hal-01185264
Contributor : Lip6 Publications <>
Submitted on : Wednesday, August 19, 2015 - 4:19:11 PM
Last modification on : Saturday, April 20, 2019 - 1:52:54 AM

### Citation

Christoph Dürr, Flavio Guíñez, Martín Matamala. Reconstructing 3-Colored Grids from Horizontal and Vertical Projections is NP-Hard: A Solution to the 2-Atom Problem in Discrete Tomography. Siam Journal on Discrete Mathematics, Society for Industrial and Applied Mathematics, 2012, 26 (1), pp.330-352. ⟨10.1137/100799733⟩. ⟨hal-01185264⟩

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