CISRA Puzzle Competition 2011 - Solutions

3C. Om Nom Nom

Avoiding the ghosts turns out to be much easier than might be expected at first glance – the rules and the maze layout virtually guarantee that the ghosts will be stuck shuffling back and forth along the bottom row. Instead, the tricky part is to collect all the letters on the bottom two rows without being caught.

It won't be possible to collect those two rows in one pass (or at least, not within the time limit). So the aim will be to get part of them early, and the rest at the end, just ahead of the ghosts. And there's very little spare time – only 5 moves can be spent travelling over empty space.

Starting out by going directly down seems tempting at first, but quickly leads to getting caught. Going left through the tunnel likewise leads to either getting caught or being too slow. There's a tantalising path through the tunnel and clearing the upper right before heading down that almost works, but the blue ghost is in the wrong spot at the wrong time.

The only path that works within the time constraints is the following one:

(Animated solution here; note that in this animation all entities move simultaneously, so the red ghost is one move ahead for the decryption step.)

The letters eaten, in order, are the following: QKWIDOOLJUQREDCOLUMNGRONSFELD. The first part is gibberish, but thereafter we get a message: RED COLUMN GRONSFELD. A little searching shows that the Gronsfeld cipher is a variant of the classic Vigenère cipher, using numbers to shift the alphabet instead of letters. The inference is that we need to decrypt the text using a set of numbers; which numbers to use are described by the remaining part of the message: RED COLUMN. We should use the column number of the red ghost to decrypt.

The red ghost's path is simple, and the respective columns numbers are 1233333456[54]32 and so forth. The columns in brackets correspond to the player passing over now-empty squares, and will not come into consideration. The decryption proceeds as follows: The first letter is Q, the first number is 1. 1 letter before Q is P, so this is the first letter in the decrypted message. Similarly, 2 letters before K is I, 3 letters before W is T, and so on.

The message thus revealed is "PITFALL HERO". The puzzle's similarity to a well known video game suggests that there should be a connection to video games, and from there it is straightforward to find out that Pitfall! is a classic video game from the '80s. The game's hero, and the answer to this puzzle, is PITFALL HARRY. The alternative of simply HARRY was also acceptable.