On the Cost of Interchange Rearrangement in Strings

  • Authors:
  • Amihood Amir;Tzvika Hartman;Oren Kapah;Avivit Levy;Ely Porat

  • Affiliations:
  • amir@cs.biu.ac.il;hartmat@cs.biu.ac.il and kapaho@cs.biu.ac.il and porately@cs.biu.ac.il;-;avivitlevy@shenkar.ac.il;-

  • Venue:
  • SIAM Journal on Computing
  • Year:
  • 2009

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Abstract

Consider the following optimization problem: given two strings over the same alphabet, transform one into another by a succession of interchanges of two elements. In each interchange the two participating elements exchange positions. An interchange is given a weight that depends on the distance in the string between the two exchanged elements. The object is to minimize the total weight of the interchanges. This problem is a generalization of a classical problem on permutations (where every element appears once). The generalization considers general strings with possibly repeating elements, and a function assigning weights to the interchanges. The generalization to general strings (with unit weights) was mentioned by Cayley in the 19th century, and its complexity has been an open question since. We solve this open problem and consider various weight functions as well.