Clique cover
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In computational complexity theory, finding a minimum clique cover is a graph-theoretical NP-complete problem. The problem was one of Richard Karp's original 21 problems shown NP-complete in his 1972 paper "Reducibility Among Combinatorial Problems".
The clique cover problem (also sometimes called PARTITION INTO CLIQUES) is the problem of determining whether the vertices of a graph can be partitioned into k cliques. Given a partition of the vertices into k sets, it can be verified in polynomial time that each set forms a clique, so the problem is in NP. The NP-completeness of clique cover follows by reduction from GRAPH k-COLOURABILITY. To see this, first transform an instance G of GRAPH k-COLOURABILITY into its complement graph G'. A partition of G' into k cliques then corresponds to finding a partition of the vertices of G into k independent sets; each of these sets can then be assigned one colour to yield a k-colouring.
[edit] References
- Karp, Richard (1972). "Reducibility Among Combinatorial Problems". Proceedings of a Symposium on the Complexity of Computer Computations, Plenum Press.
- Garey, Michael R. & Johnson, David S. (1979), Computers and Intractability: A Guide to the Theory of NP-Completeness, W.H. Freeman, ISBN 0-7167-1045-5 A1.2: GT19, pg.194.
