Instructions: After you click 'Scramble,' try to restore the numbered arrows to their correct order and orientation. Hold the mouse button and drag to select a sequence of arrows; when you release the mouse button, the selected arrows will reverse. You can also select and reverse a single arrow by clicking on it. 'Undo' undoes. The 'Undo All' button takes you back to the original scrambled configuration. The 'Solve' button, which is active only in the scrambled configuration, steps through an optimal solution (which may not be unique).

For more information see "Computing Science: Sorting Out the Genome," American Scientist, Vol. 95, No. 5, September-October 2007, pages 386-391. HTML PDF See also a related bit-player item.