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Algorithms for Solving Rubik’s Cubes

  • Erik D. Demaine
  • Martin L. Demaine
  • Sarah Eisenstat
  • Anna Lubiw
  • Andrew Winslow
Part of the Lecture Notes in Computer Science book series (LNCS, volume 6942)

Abstract

The Rubik’s Cube is perhaps the world’s most famous and iconic puzzle, well-known to have a rich underlying mathematical structure (group theory). In this paper, we show that the Rubik’s Cube also has a rich underlying algorithmic structure. Specifically, we show that the n ×n ×n Rubik’s Cube, as well as the n ×n ×1 variant, has a “God’s Number” (diameter of the configuration space) of Θ(n 2/logn). The upper bound comes from effectively parallelizing standard Θ(n 2) solution algorithms, while the lower bound follows from a counting argument. The upper bound gives an asymptotically optimal algorithm for solving a general Rubik’s Cube in the worst case. Given a specific starting state, we show how to find the shortest solution in an n ×O(1) ×O(1) Rubik’s Cube. Finally, we show that finding this optimal solution becomes NP-hard in an n ×n ×1 Rubik’s Cube when the positions and colors of some cubies are ignored (not used in determining whether the cube is solved).

Keywords

combinatorial puzzles diameter God’s number combinatorial optimization 

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Copyright information

© Springer-Verlag Berlin Heidelberg 2011

Authors and Affiliations

  • Erik D. Demaine
    • 1
  • Martin L. Demaine
    • 1
  • Sarah Eisenstat
    • 1
  • Anna Lubiw
    • 2
  • Andrew Winslow
    • 3
  1. 1.MIT Computer Science and Artificial Intelligence LaboratoryCambridgeUSA
  2. 2.David R. Cheriton School of Computer ScienceUniversity of WaterlooWaterlooCanada
  3. 3.Department of Computer ScienceTufts UniversityMedfordUSA

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