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Published online by Cambridge University Press: 12 January 2015
The minimum roman dominating problem (denoted by γR(G),the weight of minimum roman dominating function of graph G) is a variant of the verywell known minimum dominating set problem (denoted by γ(G), thecardinality of minimum dominating set of graph G). Both problems remain NP-Complete when restrictedto P5-free graph class [A.A. Bertossi,Inf. Process. Lett. 19 (1984) 37–40; E.J. Cockayne,et al. Discret. Math. 278 (2004) 11–22]. In this paper westudy both problems restricted to some subclasses of P5-free graphs.We describe robust algorithms that solve both problems restricted to (P5,(s,t)-net)-free graphsin polynomial time. This result generalizes previous works for both problems, and improvesexisting algorithms when restricted to certain families such as (P5,bull)-freegraphs. It turns out that the same approach also serves to solve problems for generalgraphs in polynomial time whenever γ(G) and γR(G)are fixed (more efficiently than naive algorithms). Moreover, the algorithms described areextremely simple which makes them useful for practical purposes, and as we show in thelast section it allows to simplify algorithms for significant classes such ascographs.