search: add topological sort helper function

[kortschak]

Fixes #78.

The naming might be contentious. The thinking is that TarjanSCC and this will end up in the structure package (that I am now thinking should be called topofor shortness) - the contents of which might look something like it does in api-explore.

We could just do a DFS toposort, but I think the value of being able to provide a reason for failure is worth any additional computational cost. The maintenance cost is 0, since we already need to look after TarjanSCC anyway.

@gonum/developers PTAL

[vladimir-ch]

Code reuse and the information returned from Sort() are a good reason to use TarjanSCC. It would be really nice if this eventually ended up in a "topo" package.

LGTM

[kortschak]

I have made minor changes - explicit statement of sort order and reversal of the order provided by TarjanSCC. I'll merge, but let me know if you disagree and I'll revert those.

[UserAB1236872]

Already merged, but seems good to me too

On Mon, Jun 8, 2015 at 10:11 PM, Dan Kortschak notifications@github.com
wrote:

Merged #80 #80.

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