Editorial for COCI '06 Regional #4 Circle

Remember to use this editorial only when stuck, and not to copy-paste code from it. Please be respectful to the problem author and editorialist.
Submitting an official solution before solving the problem yourself is a bannable offence.

The first step in solving this problem is to simulate the described transformation $K$ $K$ times in order to obtain Stanko's final circle.

The reverse transformation is not unique, but there are at most two different circles that, when transformed, yield any given circle – if we fix $B$ $B$ or $W$ $W$ as one of the pebbles, the rest are determined uniquely.

Therefore there are at most $2^K$ $2^{K}$ different possible starting circles. Since $K$ $K$ is small enough, we can check all of these and remove any duplicates.

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