Designing Small Keyboards Is Hard

  • Jean Cardinal
  • Stefan Langerman
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 2976)


We study the problem of placing symbols of an alphabet onto the minimum number of keys on a small keyboard so that any word of a given dictionary can be recognized univoquely only by looking at the corresponding sequence of pressed keys. This problem is motivated by the design of small keyboards for mobile devices. We show that the problem is hard in general, and NP-complete even if we only wish to decide whether two keys are sufficient. We also consider two variants of the problem. In the first one, symbols on a same key must be contiguous in an ordered alphabet. The second variant is a fixed-parameter version of the previous one that minimizes a well-chosen measure of ambiguity in the recognition of the words for a given number of keys. Hardness and approximability results are given.


Mobile Phone Word Pair Ambiguous Word Submodular Function Text Entry 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2004

Authors and Affiliations

  • Jean Cardinal
    • 1
  • Stefan Langerman
    • 1
  1. 1.Computer Science DepartmentUniversité Libre de BruxellesBrusselsBelgium

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