Message #2967

Subject: RE: 120Z solved!!!
Date: Fri, 07 Mar 2014 23:15:40 -0800

Finally, I’ve solved the 120-cell Mirror Z. It took me 357330 steps (happen to be an even number!). The game clock shows 38 hours and 45 minutes.

As mentioned earlier, I used some script to analyze the orbits. I found that after solving the 3C pieces, all 2C orbits are evenly permuted. So, as planned, I solved 3C first, then 2C, then 4C. 3C took about 19 hours and 85k moves; 2C about 2 hour and 24k moves; and 4C about 17.5 hours and 248k moves. 2C pieces were indeed easy after 3C were solved.

I have to admit that this time I went too deep using computer. I used a parity fixing strategy found by the script for 3C orbits: flipping 19 cells changes the parity of seven 3C orbits which pass through one cell. This is the most powerful 3C parity algorithm I’ve found. Without computer I’d have a hard time finding such 19 cells. I used this algorithm several times towards the end of the 3C step. I’m certainly not proud of it. But it’s hard not to look at the 19 cells when the script has already generated it.

As before, I used a monitoring script to keep track of progress so that I know it when I screw up things. I also used Git to backup the macro and log files.

Scripts and files are dumped into this github repo:

I’ve never organized the script though…

Andrey, thank you for making this puzzle! Also, if you didn’t solve the puzzle, I wouldn’t even know how delicate this puzzle was and I wouldn’t even attempt it.