MY solution would be to sort the web log by date, and IP. If the user made less than 2-page sequence, then remove that IP. For each 3 possible sequence, add it to a data structure. If the sequence already exists, then increment the count of the sequence. In the end, you can do a search on the data structure to find the 3-page sequence that appeared the most frequent.

Could you use a hash table where the key is derived from the sequence and the value is the number of times it occurs?