Doshu Puzzle

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Object: Make the yellow and red tokens swap places.
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Contributed by: Karl Scherer (April 2014)
Open content licensed under CC BY-NC-SA
Snapshots
Details
Pink and light yellow floor tiles indicate where the round tokens have to end up. If all tokens have swapped places, you get a win message at the top border. Some challenges show one or more additional black walls. You cannot move into or through a wall.
Drag slowly
Take care to execute the dragging of a token slowly, otherwise the second token that is supposed to be dragged along with it might be left behind, which is against the rules of this puzzle. If the adjacent token lags behind, you can click the "undo" button to take the last move back (see below).
Controls
"challenge":
You can select between 33 fixed setups and nine randomized setups.
"prev," "next" setter bar:
Click to select the previous or next challenge.
"reset":
Takes you back to the starting position. In the scrambled challenges, this means that you see the previous scrambling. To see a differently randomized setup for this challenge, select a different challenge, and then select the desired challenge again (use "<," then ">").
"moves":
Counts the moves; useful when you compete for the fastest solution with your friends.
"undo":
Click to take the last move back.
History
This puzzle was previously published as the Zillions game "Doshu" by the same author.
Permanent Citation
"Doshu Puzzle"
http://demonstrations.wolfram.com/DoshuPuzzle/
Wolfram Demonstrations Project
Published: April 28 2014