an old worn interview question

"given a graph of pointers, can you find a loop there"

I must admit that during 20 or so years of programming I never came
across any practical program that required finding a loop in the
directed graph. I suspect that finding a loop is really a part of
bigger task such as finding transitive closure of a graph. And the
tricks of finding a single loop provide no insight how to solve bigger
problem. So, any counter examples of an interesting problem, or an
algorithm that requires finding a single loop in the graph?

.

Relevant Pages

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