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Four quarters are placed at the corners of a square table. The quarters can be any combination of heads and tails. You are allowed to look at the quarters, then they are covered with four identical plastic cups.
The following scenario is now repeated. You are blindfolded and the table is rotated randomly. You may now look at any two of the quarters and flip neither of them, either of them, or both of them and then the cups are replaced.
Find an algorithm that guarantees that you will eventually end up with all heads or all tails.
The solution will be posted shortly.
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