Linear time algorithm for computing the rank of divisors on cactus   graphs
  Rank of divisor on graph was introduced in 2007 and it quickly attracts many attentions. Recently, in 2015 the problem for computing this quantity was proved to be NP-hard. In this paper, we describe a linear time algorithm for this problem limited on cactus graphs. 
Phan Thi Ha Duong
math.CO cs.DM cs.DS