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

  • Authors:
  • Christoph Dürr;Flavio Guiñez;Martin Matamala

  • Affiliations:
  • christoph.durr@lip6.fr;flavio.guinez@gmail.com;mmatamal@dim.uchile.cl

  • Venue:
  • SIAM Journal on Discrete Mathematics
  • Year:
  • 2012

Quantified Score

Hi-index 0.00

Visualization

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.