In this paper we extend Pukhlikov--Khovanskii type presentation to the case of K-theory of toric and flag varieties. First we study the Gorenstein duality quotients of the group algebra of free abelian group (possibly of infinite rank). Then we specialize to the K-ring of integer (virtual) polytopes with a fixed normal fan. Finally we show that the K-theory of toric and flag varieties can be realized as polytope K-rings and describe the classes of toric orbits or Schubert varieties in them.
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