A Combinatorial, Strongly Polynomial-Time Algorithm for Minimizing   Submodular Functions
  This paper presents the first combinatorial polynomial-time algorithm for minimizing submodular set functions, answering an open question posed in 1981 by Grotschel, Lovasz, and Schrijver. The algorithm employs a scaling scheme that uses a flow in the complete directed graph on the underlying set with each arc capacity equal to the scaled parameter. The resulting algorithm runs in time bounded by a polynomial in the size of the underlying set and the largest length of the function value. The paper also presents a strongly polynomial-time version that runs in time bounded by a polynomial in the size of the underlying set independent of the function value. 
Satoru Iwata (Fields Institute), Lisa Fleischer (Columbia University),   Satoru Fujishige (Osaka University)