A general treatment of the spectral problem of quantum graphs and
tight-binding models in finite Hilbert spaces is given. The direct spectral
problem and the inverse spectral problem are written in terms of simple
algebraic equations containing information on the topology of a quantum graph.
The inverse problem is shown to be combinatorial, and some low dimensional
examples are explicitly solved. For a {\it window\ }graph, a commutator and
anticommutator algebra (superalgebra) is identified as the culprit behind
accidental degeneracy in the form of triplets, where configurational symmetry
{\it alone\ }fails to explain the result. For a M\”obius cycloacene graph, it
is found that the accidental triplet cannot be explained with a superalgebra,
but that the graph can be built unambiguously from the spectrum using
combinatorial methods. These examples are compared with a more symmetric but
less degenerate system, i.e. a {\it car wheel\ } graph which possesses neither
triplets, nor superalgebra.
