Bob is busy saving the world on Stackexchange by monitoring down yet one more super-vilain. Alice rushes in holding a protracted paper.

A: I made a discovery you’ll like.

B: I’m not on fb.

A: Whatever. You have most likely seen 3-D or 4-D labyrinths. But have you ever seen a 1-D labyrinth?

B: 1-D? That can’t be a lot of a problem, can it?

A: It can. Look right here, I’ve a map.

ab A bcefgi B acdfghi C bcfgi D bcdg E cefh F efghi G begi H dehi I bcdfgij J j

B: That’s a map? A single line?

A: What did you count on? It is a 1-D labyrinth!

B: Hm… OK, perhaps. How does it work?

A: It is the entry to an deserted top-secret operations base.

B: These issues do not exist!

A: Exactly that sort! The entry is a protracted tunnel. There are loads of checkpoints and heavy doorways managed by buttons. The buttons are all over. Normally they’re operated by guards. But these are gone.

B: If they’re gone, how are you going to open the doorways?

A: That is why I want you. Look on the map. The uppercase letters are the heavy doorways. The lowercase letters are the buttons working the corresponding door. You elevate a door by urgent the button. You should preserve urgent the button or the door slams shut instantly. Some buttons could be operated from outdoors. I want you to press these buttons so I can cross the primary doorways. Then I press another buttons inside and also you cross the doorways.

B: Isn’t it, like, harmful?

A: No…. I do not assume so… And it’s thrilling! I wish to see if collectively we handle to go all doorways. Every time you open a door it offers entry to new buttons. It is sure to steer someplace. Let’s go and have a strive!

B: I’ve a greater concept. I’ll simply put the “map” on Stackexchange and they’re going to crack it very quickly.

So expensive puzzler, can to assist Alice and Bob cross the tunnel?

ab A bcefgi B acdfghi C bcfgi D bcdg E cefh F efghi G begi H dehi I bcdfgij J j

Alice and Bob enter from the left. One of them strikes one place at a time. To go a door (an uppercase letter), the opposite participant should stand at a corresponding button (the lowercase letter). If a participant leaves a button it shuts the door, probably killing anybody standing below the door. The objective is to carry Alice and Bob safely to the proper.