http://www.eternityii.com/It's an
edge matching puzzle(believed to be
NP-Complete), but is apparently solvable. The challenge is to find some form of weakness or property of the tiles that can lead to a significant reduction in the size of the problem.
For those who are unaware of such problems, the growth is
exponential, so placing 160 tiles is achievable in a matter of seconds, 170 in a matter of minutes, 189 in a matter of hours, 190 in a matter of days and 192 in a matter of years. Exponential growth means you can not find a solution with brute force alone, but if you can find a property that makes this a special case then you can create a
polynomial time algorithm.
And before you suggest it (and assume the problem is easy), remind yourself of the problem class; there are countless experienced mathematicians and computer scientists working on it already - it is by no means trivial!
