Chaining of Maximal Exact Matches in Graphs

We show how to chain maximal exact matches (MEMs) between a query string $Q$ and a labeled directed acyclic graph (DAG) $G=(V,E)$ to solve the longest common subsequence (LCS) problem between $Q$ and $G$. We obtain our result via a new symmetric formulation of chaining in DAGs that we solve in $O(m+n+k^2\mathrm{\mid }V\mathrm{\mid }+\mathrm{\mid }E\mathrm{\mid }+kN\log N)$ time, where $m=\mathrm{\mid }Q\mathrm{\mid }$, $n$ is the total length of node labels, $k$ is the minimum number of paths covering the nodes of $G$ and $N$ is the number of MEMs between $Q$ and node labels, which we show encode full MEMs.