Shorter solution for Robozzle puzzle no 132 - Split

Question

I wonder a shorter solution for Robozzle puzzle number 132, "Split."

Puzzle is shown below. I have solved it but I'm wondering shorter solution for this and there many exist.

Basically, the rocket has to collect stars.

You give certain commands to the rocket and it obeys them. The less command, the better. Commands for this puzzle are shown below.

Commands are displayed on bottom right corner. From top to down they are: go straight, turn left, turn right; execute F1 function, execute F2 function; execute this command no matter what the colour of cell is, execute this command in red cell and execute this command in green cell.

Each time it starts with F1 function. If you don't call F2 function in F1 then it will not execute commands in F2.

Let me show you how to play this game in another easy puzzle.

This puzzle is called "Stairs." You can see the commands and given function on the bottom right corner again. They are blank. If I click on Go! nothing happens because there are no commands given in function.

Now, let's fill in the function with some necessary commands.

You can see where robot stays. It hasn't collected all the stars. Function was called but it was executed just once. Why? Because there is no iteration (or recursion) or repetition of commands.

Remember we need to collect all the stars, so let's call F1 function again at the end of commands so that it iterates (or recurses) or repeats itself.

The rocket has collected all the stars because F1 was called again at the end so that it repeatedly goes beginning when it finishes executing all the commands. At the bottom you can see what the next steps are such as turn left, go, turn right and F1. This was completed in 5 commands (or steps).

Now, hoping that you understood the fundamentals of this puzzle let me show you my longer solution for Robozzle puzzle number 132 - "Stairs". It contains 11 commands (or steps).

I screenshot it during the execution of commands so that you can see the upcoming steps (or commands) on bottom command line. I directly called F2 because F1 was very short. In F2 I turned 180 degree back, stepped forward, turned 180 degree back again, and stepped forward twice. I repeated these steps as long as the cells were blue. After blue cells I put turn right on green and go straight on any colour.

Basically, I stepped back once and stepped forward twice. Repeated this action (or recalled F2) as long as the rocket was in blue cells. Since there were a lot of blue cells, the F2 called itself again and again postponing the commands (or steps) I entered after F2 there: turn right on green and go straight on any colour. As far as I know this is called "stacks" (or "stacking") in programming. You can see them piled up on the command line at the bottom of the image. When the rocket arrives at the green cell it gives up calling F2 and executes the stack or piled steps after F2: it turns right on the green cell and goes straight. It ignores turn right on green afterwards. Why? Because there are no green cells except the corner.

My solution contains 11 commands (or steps). I'm looking for a shorter solution for this Robozzle "Split" puzzle: http://www.robozzle.com/js/play.aspx?puzzle=132.

There exist 7 command (or 7 step) solution.

Answer 1

7 commands:

Explanation:

The function F2 is called repeatedly. F2 steps forward N times until not on a blue position, turns right if the end position is green, then does a $180^\circ$ turn N times. F2 uses recursion to count the number of steps N.

In the first execution, N=8. Since this is even, the $180^\circ$ steps do nothing in total, and with the green right turn, the bot ends facing right. In the second and third executions, N=5. Since this is odd, the $180^\circ$ steps are equivalent to one $180^\circ$ turn. So the bot turns $180^\circ$ at the red square, and ends facing left. After returning to the green square, the bot does the green right turn followed by a $180^\circ$ turn, and in total turns from left to down. The fourth execution of F2 finds the second star, winning.

Answer 2

Here is another 9-command solution:

Answer 3

Below is a 9-command solution.

And here is a more elegant recursive 10-command solution.

But what you wanted is a 7-command solution. Here it is:

... but as I post this I see aschepler posted it hours ago...

Answer 4

Really cool game. My solution isn't that elegant, but hey. Managed to whittle down this:

To this: