Presents a global approach to solve the three-layer wirability problem for knock-knee layouts. In general, the problem is NP-complete. Only for very restricted classes of layouts polynomial three-layer wiring algorithms are known up to now. The authors show that for a large class of layouts a three-layer wiring can be constructed by solving a path problem in a special class of graphs or a two-satisfiability problem, and thus may be wired in time linear in the size of the layout area. Moreover, it is shown that a minimum stretching of the layout into a layout belonging to this class can be found by solving a clique cover problem in an interval graph. This problem is solvable in time linear in the size of the layout area as well. Altogether, the method also yields a good heuristic for the three-layer wirability problem for knock-knee layouts.
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