public static Solution GBFS(State startState, State endState, Func<State, State, int> heuristic, bool considerDepth=false)
        {
            Stopwatch watch = Stopwatch.StartNew();
            Tree<State> tree = new Tree<State>(startState);
            HashSet<Node<State>> openSet = new HashSet<Node<State>>();
            PriorityQueue<Node<State>> fringe = new PriorityQueue<Node<State>>();
            HashSet<int> closedSet = new HashSet<int>();

            Node<State> currentNode = tree.Root;
            int expandedNodes = 0;
            while(currentNode != null && !currentNode.Data.Equals(endState))
            {
                if (watch.ElapsedMilliseconds > (1000 * 60 * 5))
                    break;
                //expand this node and add it to the closed set + remove it from the open set
                expandedNodes++;
                closedSet.Add(currentNode.Data.GetHashCode());
                openSet.Remove(currentNode);

                //consider all nodes we can get from here that are not in the closed set
                IEnumerable<Node<State>> successors = currentNode.Data.GetAllMoves().Where(s => !closedSet.Contains(s.GetHashCode()))
                    .Select(d => new Node<State>(d, currentNode));

                //add them to the tree, and the open set
                //also keep track of the new nodes
                foreach(Node<State> successor in successors)
                {
                    currentNode.Children.Add(successor);
                    openSet.Add(successor);
                    fringe.Add(heuristic(successor.Data, endState) + (considerDepth? successor.Depth() : 0), successor);
                }

                //get the first node that has a heuristic value equal to the lowest heuristic value in the fringe and make that our current node
                currentNode = fringe.Pop();
            }

            watch.Stop();
            //no solution possible
            if (currentNode == null)
                return new Solution((List<State>)null, expandedNodes, watch.ElapsedMilliseconds, tree.Size(), false);

            //so now we've reached the final state, so return the solution
            return new Solution(tree.BacktrackFrom(currentNode), expandedNodes, watch.ElapsedMilliseconds, tree.Size());
        }