Any problem that has only finitely many possible inputs can be solved in O(1) time on a standard RandomAccessMachine by including a very large table of all possible inputs and the corresponding output for each. An example of such an algorithm in real life is the usual implementation of isspace, isalpha, and similar macros in the standard C library. In practice, you should probably use table lookup only if the table is small, frequently used, and computing individual values at run-time takes long enough the precomputation pays off.