Browsing by Author "Obscura Acosta, Nidia"
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Obscura Acosta, Nidia (2018)In this thesis we study the concept of “safe solutions” in different problems whose solutions are walks on graphs. A safe solution to a problem X can be understood as a partial solution common to all solutions to problem X. In problems whose solutions are walks on graphs, safe solutions refer to walks common to all walks which are solutions to the problem. In this thesis, we focused on formulating four main graph traversal problems and finding characterizations for those walks contained in all their solutions. We give formulations for these graph traversal problems, we prove some of their combinatorial and structural properties, and we give safe and complete algorithms for finding their safe solutions based on their characterizations. We use the genome assembly problem and its applications as our main motivating example for finding safe solutions in these graph traversal problems. We begin by motivating and exemplifying the notion of safe solutions through a problem on st paths in undirected graphs with at least two nontrivial biconnected components S and T and with s ∈ S, t ∈ T . We continue by reviewing similar and related notions in other fields, especially in combinatorial optimization and previous work on the bioinformatics problem of genome assembly. We then proceed to characterize the safe solutions to the Eulerian cycle problem, where one must find a circular walk in a graph G which traverses each edge exactly once. We suggest a characterization for them by improving on (Nagarajan, Pop, JCB 2009) and a polynomialtime algorithm for finding them. We then study edgecovering circular walks in a graph G. We look at the characterization from (Tomescu, Medvedev, JCB 2017) for their safe solutions and their suggested polynomialtime algorithm and we show an optimal O(mn)time algorithm that we proposed in (Cairo et al. CPM 2017). Finally, we generalize this to edgecovering collections of circular walks. We characterize safe solutions in an edgecovering setting and provide a polynomialtime algorithm for computing them. We suggested these originally in (Obscura et al. ALMOB 2018).
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