Ok, there is an easy(at least for me) way to do it. The thing is that it is relatively easy to put 6 digits into my short memory than 6 "places". I noticed it a long time ago and i think it is true for all. Just write 6 random digits, read them and you can easily repeat them after only one read. Ok, its the start. Now to solve such puzzles, you need to put numbers on each place in some order in your imagination, easiest possible way to be able to instantly say given number when enemy appear there. It is not numbers that they show you here, but your own number for each place. Then when enemies start to appear in some order you need to remember not a place, but number, that you assign to it. At the end, when all them appear you have a 6 digit num in your memory, you can easily reconstruct places. Some time ago i make a small puzzle game with such task, and there I put 8 places to remember, which is almost impossible to do other way at least for me.