class A_Star(object):
    def __init__(self, starts, goals, h, d, neighbors):
        """
        :param h: heuristic function
        :param d: cost from node to node function
        :param neighbors: neighbors function
        """
        open_set = []
        g_score = {}
        f_score = {}

        for start in starts:
            open_set.append(start)
            g_score[start] = d(0, start)
            f_score[start] = h(start)

        while open_set:
            open_set.sort(key=lambda node: f_score[node])
            current = open_set[0]

            if current in goals:
                self.cost = g_score[current]
                break

            open_set = open_set[1:]  # remove current

            for neighbor in neighbors(current):
                tentative_g_score = g_score[current] + d(current, neighbor)
                if neighbor not in g_score or \
                   tentative_g_score < g_score[neighbor]:
                    g_score[neighbor] = tentative_g_score
                    f_score[neighbor] = g_score[neighbor] + h(neighbor)
                    open_set.append(neighbor)