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There is a certain family of typical branch & bound problems in which we have to put $n$ objects into $m$ indistinguishable bags.

Usually solutions are represented by $n$-size vectors in which $V[i]$ means that the $i$-th element is in the $V[i]$-th bag.

Is there a way to avoid generating equivalent solutions without performing an $\mathcal{O}(n)$ time check once the potentially equivalent solution has been built?

I was trying to do something similar as when avoiding circular permutations, but no adaptations seems to work.

Nick
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Álvaro G. Tenorio
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1 Answers1

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You could impose a canonical ordering on the bags.

For instance, in each bag find the lowest-numbered item in that bag, and imagine labelling the bag with that number. Now add the additional constraint that to be a valid solution, the bags must be in sorted order according to their label. In other words, the label on the $i$th bag must be less than the label on the $i+1$st bag.

If you can express this constraint within your system, it ensures that each equivalent solution will be generated only once.

D.W.
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