UniformCostSearch for Berkeley Pacman project1

Question

So I am trying to make the pacman project from Berkeley and the UniformCostSearch function works except for one test and I am not very sure what the problem is. *** student solution: ['Right', 'Down', 'Down'] *** student expanded_states: ['A', 'B', 'D', 'G']

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*** correct solution: ['Right', 'Down', 'Down'] *** correct expanded_states: ['A', 'B', 'D', 'C', 'G']

This is the code:

def uniformCostSearch(problem: SearchProblem):
    """Search the node of least total cost first."""
    "*** YOUR CODE HERE ***"

    node = {'state': problem.getStartState(), 'cost': 0}
    if problem.isGoalState(node['state']):
        return []

    # Folosesc PriorityQueue
    # In frontier pun nodurile intalnite dar care nu o fost explorate
    frontier = util.PriorityQueue()
    frontier.push(node, 0)
    # In explored pun nodurile care o fost deja explorate
    explored = set()

    while True:
        if frontier.isEmpty():
            raise Exception('Search failed!')

        # Luam nodu din frontier ca sa il exploram
        node = frontier.pop()

        # Daca nodu o fost deja explorat dam skip la ieratia curenta
        if node['state'] in explored:
            continue

        # Reconstruim calea pana la Goal folosindu ne de parent si ne tot intoarcem in spate
        explored.add(node['state'])
        if problem.isGoalState(node['state']):
            actions = []
            while 'parent' in node:
                actions.append(node['action'])
                node = node['parent']
            actions.reverse()
            return actions

        # Obtinem succesorii urmatoarei stari
        successors = problem.getSuccessors(node['state'])
        for successor in successors:
            child = {'state': successor[0], 'action': successor[1], 'cost': successor[2], 'parent': node}
            if child['state'] not in explored:
                frontier.push(child, child['cost'] + node['cost'])