# (Game of Life) It's so fragile… but how to reach it?

Seeing as how other questions on Conway's Game Of Life were received quite well, I was inspired to make my own. The concept of having a 'base' and trying to accomplish an aim seems like such a fun game! Well I won't ramble on any longer (actually I will at the end) - here's the puzzle:

Given the green area, annihilate all cells in the grid

or, in cooler words, in the spirit of these puzzles

Construct a rocket to destroy the sun and annihilate all life in the universe

Rules:

• No cells may remain at the end i.e runaway gliders count as living
• You may only alter the green cells at generation 0; you may not do anything once the simulation begins

I also strongly recommend getting a good simulator - Golly is pretty good

Notes: I just can't resist pointing out how fragile the sun is. Add a square, and it dies. Take away a square, and it dies. Do anything, and it dies. But the green area is really far away...

Some help needed:

• Is it possible to permanently highlight cells (in Golly)?
• How do you make a gif of the animation?

Challenge: Shift the green area down, say 100 squares. Try it now!

Although this question has been solved, don't be discouraged from continuing to try as the process of finding a solution is quite fun (at least it was for me), and unique solutions are rare. And plus the challenge is still out there

Inspiration

• I have seen what people can do with the Game of Life but I have never seriously played with it. Is there any way to solve this by reasoning or is it just add things until it works? – FrodCube Jan 2 '17 at 13:24
• @FrodCube I believe there are two ways to solve this: brute-force or trial and error; and trial and error was pretty fun for me. '...finding a good construction all by yourself is fun (at least it was for me).' - BaSzAt – Wen1now Jan 3 '17 at 1:12

Here's a 17-cell solution that works at any distance:

Initial pattern on the left, GIF animation on the right:

I bet this (or something very similar) is the solution you were expecting. It consists of:

a lightweight spaceship that first collides with the phoenix oscillator and turns it into a block, followed by a middleweight spaceship that destroys the block. In the initial configuration, both spaceships have their sparks removed to reduce their width and cell count.

This solution takes 2×n + 32 steps to destroy the target, where n is the number of rows between the starting area and the target oscillator. In your baseline puzzle, n = 7, so the target is destroyed in 46 steps. Note that n must be an odd number for the solution to work exactly as shown above. However, it can be made to work for even values of n simply by shifting the pattern down by one row within the starting area. This, of course, delays the destruction by two additional steps.

Given the way your bonus challenge was phrased, and the shape of the starting area, I figured you might have had a solution like this in mind. Based on that guess, I found the actual solution by manual trial and error:

First, I tried all the possible collision with a single LWSS, MWSS or HWSS; this didn't take very long, since there are only four distinct options for each spaceship type, depending on whether it starts an even or an odd number of squares away from the target, and whether the spark side is on the left or on the right.

Alas, none of those 12 possible single-spaceship collisions made the target vanish completely without a trace, but a couple of them only left a few simple still lifes, including one that left just a single block right in front of the starting area. Since there was still room in the starting area for another spaceship, I then tried taking that collision and adding a second trailing spaceship to see if it might be able to make the block disappear. And indeed, it turns out that it can.

• Nice work! That was indeed my solution. It took me a few hours to find though, including editing the starting area – Wen1now Jan 12 '17 at 1:12

I have found this solution (35 gens):

Animation: