Two robots are to be parachuted onto random locations on an infinite line. When they land, their parachutes detach and remain where they are. The robots may each be programmed with numbered instructions from the following set:

• Go left one unit
• Go right one unit
• Skip next instruction unless there is a parachute here
• Go to (label)

Each instruction takes one cycle to execute. Program the robots to collide.

Notes:

There must be a finite number of lines of code (ie, you can't say move right once, then left twice, then right thrice, .. ad infinitum).
Try to do it using the fewest lines of instructions (if both robots have the same instruction set, you can count it only once).
There is no way for the robots to distinguish between the two parachutes if they are crossed.

The instructions in the program are numbered, and are executed in order. An instruction of "go to" some label means that the next instruction to follow will be at that number, and continue from that point in numerical order.
For example, look at the following:

10  right one unit
20  left one unit
30  go to 10
40  do a backflip

This code would have the robot forever going back and forth between two spots.
Line 10 would execute, then 20, then 30, and then back to 10 (line 40 in this example would never be run).

(In reply to re: Pretty good by Brian Wainscott)

Thanks Brian,

And to address why the "extra" line was in there... it was because I initially had the 2nd robot do nothing more than move to the right (with a 2-line program).

If we don't have this clause in the original problem (namely, that "if both robots have the same instruction set, you can count it only once"), then we can minimize one Robot's code to two lines (as I initially did). In that case, this "extra" line is needed to catch up to the short-program-robot.

So, with the clause... 6 lines... so far... and without the clause 7 + 2 = 9 lines of code.

--- SK

Posted by SilverKnight on 2003-09-11 16:25:32