I have a set of objects. Each has a 'depends_on' list (of other objects) and a 'depended_upon_by' list. The lists are symetric - A is on B's 'depends_on' list IFF B is on A's 'depended_upon_by' list. There are no cycles; no object is on its own lists.

I want to sort the list into ranks. The first rank should have all the objects with empty 'depends_on' lists. No object can be in the same rank with another object in its 'depends_on' list. Each object is in as low a rank as possible, without violating the forgoing constraints. I can think of several algorithms that would do this. Mainly,
* Everybody tracks their current rank
* Start everybody off in the first rank,
* Everybody adds 1 to their current rank and tells all their 'depended_upon_by's that they have to be at least that high.
* If an object is told to be at least N, if they aren't already N, they increase their rank to N and tells their 'depended_upon_by's to increase to at least N+1.

And I can think of both recursive and iterative ways to do this. But I have this nagging feeling that there's something really compact and elegant using sort. I just can't think what it would be.

Anybody?<p thanks

In reply to Partial sort for dependency graph by throop

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