Recently I read a seminar work which says:
The matching algorithm [for general graphs] can be extended
to the weighted case, which appears to
be one of the “hardest” combinatorial
optimization problems that can be
solved in polynomial time.
Immediately the following question came to my mind:
Do you know other “P-hard” problems?
For now I would like to define P-hard as: “A polynomial algorithm was found very late (after 1950) in the literature for that problem”. (Or how could one better define “hard” if there is already a deterministic algorithms which solves the problem in polynomial time?)
There are actually “P-complete” problems, which means that every other problem that can be computed in polynomial time can be reduced to them. See http://en.wikipedia.org/wiki/P-complete.