util.py

class Node:
    def __init__(self, state, parent, action):
        self.state = state
        self.parent = parent
        self.action = action


# Not applicable due to inefficiency for this use case
class StackFrontier:
    def __init__(self):
        self.frontier = []

    def add(self, node):
        self.frontier.append(node)

    def contains_state(self, state):
        return any(node.state == state for node in self.frontier)

    def empty(self):
        return len(self.frontier) == 0

    def remove(self):
        node = self.frontier[-1]
        self.frontier = self.frontier[:-1]
        return node


class QueueFrontier(StackFrontier):
    def remove(self):
        node = self.frontier[0]
        self.frontier = self.frontier[1:]
        return node