This problem had been studied by Euler. Rearrange the colored
letters below so that each row or column will have four distinct letters having four
This puzzle is
INTERACTIVE in Java-enabled browsers.
Clicking on any white
cell will interchange its content with the content of the green cell.
Use this method repeatedly as you rearrange the letters. For example, to move the
RED A in
the second row to the fourth cell of the last row, click on the
RED A, then
click on the the fourth cell of the last row.
here for a non-Java page