For one of their clients, ACM prepares a TV advertisement that features ancient heroes, for example Prometheus, Achilles, Odysseus and many others. To demonstrate how difficult was life for these heroes, ACMruns computer simulations of their most famous tasks. In this problem, we will try to solve the problem of Theseus.
Theseus was an Athenian hero who killed Minotaur, the half-man, half-bull monster residing in an inescapable Labyrinth constructed by Daedalus. The hardest part of Theseus’ task was not killing the monster — the legend says Minotaur was just sleeping when Theseus came to him. Thus, the hero was able to batter the monster with his bare hands. But then the real challenge came: to find the way out. As you may know, Ariadne, beautiful daughter of king Minos, played an important role in this part. But that’s a different story.
As the technology advanced a lot since the ancient times, there are several important differences in today’s simulations:
1. Labyrinth-making skills advanced as well. Two-dimensional labyrinths are not a big challenge anymore. Thus, our labyrinth is d-dimensional. It looks like a regular ”grid” of n1×n2×. . .×nd (hyper)cubes, each of them being either empty (corridor) or filled with a rock (wall). Theseus moves in steps, each step means travelling between two neighboring empty hypercubes in any dimension. Two hypercubes are considered neighboring, if and only if the difference in their
space coordinates is exactly one in one dimension, and zero in all other dimensions.
2. Our Minotaur is stronger, thus, it is no more possible to batter him with bare hands. Theseus must use a sword which lies somewhere inside the labyrinth. Note that before he takes the sword, he cannot go through the hypercube where Minotaur resides!