Frontier and Hashtable
In Aima 3/e we have these two sentences in the book (chapter 3)
1- "expand the chosen node adding the resuting node to the frontier
only if not in the frontier or explored set"
2-"The explored set can be implemented with a hash table to allow efficient checking for repeated states"
Now, my question is: what about the frontier? we must check the frontier for repeated states, but this set is a queue, not a hashtable!! can we chech the frontier for repeated states efficiently? how?
I think this is a natural question that might be arise for every reader!
Thanks a lot