这是我在这里的第一篇帖子，我是一个Python初学者，正在为学校项目工作。

我的具体问题是伯克利吃豆人项目1的一部分： https://inst.eecs.berkeley.edu/~cs188/sp19/project1.html

在BFS部分我遇到了麻烦。特别是在tinyMap上，当我的程序处于2,2状态时，它正常过渡到2,3，但2,1有一个额外的北方向。

successorsVisited是一个坐标状态的集合，myQueue是一个普通队列，problem是棋盘，getSuccessors返回一个元组列表（状态，方向，成本），我在将其推回队列之前将其编辑为（状态，方向，成本，路径）。

请假设我已经正确处理了基本情况，这是从队列中开始的5,4和4,5的迭代步骤。

def BFS_Helper(problem,myQueue,successorsVisited):    while not myQueue.isEmpty():        node = myQueue.pop()        state = node[0]        for x in range(0,len(problem.getSuccessors(state))):            aTuple = problem.getSuccessors(state)[x]            if aTuple[0] not in successorsVisited:                successorsVisited.add(aTuple[0])                node[3].append(aTuple[1])                bTuple = (aTuple[0], aTuple[1], aTuple[2],  node[3]) # new bTuple with path = path + action                 print(bTuple)                if problem.isGoalState(aTuple[0]):                    return bTuple[3]                myQueue.push(bTuple)    return BFS_Helper(problem, myQueue,successorsVisited)

我在检查目标状态之前打印出bTuple，以下是打印输出。加粗的北方向是我的问题，我无法弄清楚它是如何发生的。

((5, 3), ‘South’, 1, [‘South’, ‘South’])

((3, 5), ‘West’, 1, [‘West’, ‘West’])

((4, 3), ‘West’, 1, [‘South’, ‘South’, ‘West’])

((2, 5), ‘West’, 1, [‘West’, ‘West’, ‘West’])

((4, 2), ‘South’, 1, [‘South’, ‘South’, ‘West’, ‘South’])

((1, 5), ‘West’, 1, [‘West’, ‘West’, ‘West’, ‘West’])

((3, 2), ‘West’, 1, [‘South’, ‘South’, ‘West’, ‘South’, ‘West’])

((1, 4), ‘South’, 1, [‘West’, ‘West’, ‘West’, ‘West’, ‘South’])

((2, 2), ‘West’, 1, [‘South’, ‘South’, ‘West’, ‘South’, ‘West’, ‘West’])

((1, 3), ‘South’, 1, [‘West’, ‘West’, ‘West’, ‘West’, ‘South’, ‘South’])

((2, 3), ‘North’, 1, [‘South’, ‘South’, ‘West’, ‘South’, ‘West’, ‘West’, ‘North’])

((2, 1), ‘South’, 1, [‘South’, ‘South’, ‘West’, ‘South’, ‘West’, ‘West’, ‘North’, ‘South’])

((1, 1), ‘West’, 1, [‘South’, ‘South’, ‘West’, ‘South’, ‘West’, ‘West’, ‘North’, ‘South’, ‘West’])

非常感谢您的任何帮助。

回答：

您的问题原因在这里：

node[3].append(aTuple[1])

当循环遍历后续状态的迭代次数增加时，这将成为一个问题。在这些迭代中，使用的是同一个 node[3]… 它仍然包含来自先前迭代的附加值，您又向其中添加了另一个值。

解决方案：不要修改 node[3]。相反，动态创建一个新列表：

bTuple = (aTuple[0], aTuple[1], aTuple[2],  node[3] + [aTuple[1]])