Who Cares About Complexity?
Tic-tac-toe is an example of an exponential search space (<= 99 states fully expanded).
In practical terms O(2n) is intractable. In other words for realistic values of n, the problem cannot be solved in reasonable (any) amounts of time/space.
Most AI problems involve exponential search.
- E.g. avg. branching factor in chess is 35, average moves =50/player: 35100 states.