def graph_search(problem, queue_type):
	frontier = util.Queue()
	explored = set()
	start_state = problem.getStartState()
	frontier.push(start_state)
	while True:
		if frontier.isEmpty(): return None
		node = frontier.pop()
		if problem.isGoalState(node): return node
		explored.add(node)
		for s in problem.getSuccessors(node):
			if s not in explored:
				frontier.push(s)