[Death by Mirrors]

@Lilith Dracania

Do you know the game Mastermind? It's the same procedure.

There is a secret code you don't know yet. This can be any combination of the colors blue, purple, red and yellow. For example your code might be blue blue red purple. But since you aren't actually told what it is, you need to figure it out by guessing combinations.

Say you guess yellow purple red yellow. Then you receive a reply of 2 colors, 1 location - because when compared with the aforementioned example, there is no yellow in the code you're supposed to guess. There is however a purple and a red, so you already guessed two colors. One of these two, red, is also at the exact location you guessed.

But of course from that alone you can't figure out yet what exactly the correct colors are. That's why you guess again. Say your next guess is yellow yellow red red. Now you have 1 color, 1 location. Whoops - what happened? That purple you took away has to be part of the solution, it seems. You now also know that the code contains either red or yellow, but not both (otherwise you would have gotten 2 correct colors from your second guess). It also neither contains two or more red, or two or more yellow (again, if it did, you'd have received 2 color as a reply).

You decide to go with yellow, and you know for certain there is a purple in there. So your next guess is yellow purple purple purple, which still yields 1 color, 1 location. Now you know that there can't be more than one purple, and also (since you already established the code contains at least one purple) yellow isn't part of the solution. Therefore you know it is one purple, one red, and the rest has to be blue.

You take a look at your first guess again and see either the second color is purple, or the third color is red. You compare it with your second guess. If the second color is purple, then red has to be the fourth, meaning the solution is blue purple blue red. If instead the third color is red, purple has to be the fourth, meaning the solution is blue blue red purple. You don't know yet which of the two possibilities is correct, but you already have a 50% chance of picking the right one. If you do, you solved the puzzle and start over with a new code. If you picked the wrong one of the two by chance, just submit the other with your next guess, and you've also moved on to the next puzzle with a new code.