This is a rehash and considerable simplification of Programming Challenge 32 which had no entries.
Using 6 characters (4 corners and a horizontal and vertical) your code has to construct loops; those are rectangular types shapes. The longer the shape the more points scored and the loop characters are removed leaving space for more loops.
However the grid area is only 18 x 7 and there are 10,000 characters and you have to place every character on the grid. If or more likely when the grid gets full, your program stops. That's it!