Question

我试图实施I.A.解决Water Jugs问题的广度优先搜索算法，但我遇到了这个问题：

每次我向数组添加一个新元素时，它都会更改数组中的所有元素。就像它一样。

换句话说......

＆＃34;边疆＆＃34;数组正在改变每个＆＃34; jug＆＃34;之间的所有元素。函数调用。

有人可以分享一些有关此代码的见解吗？

（我更担心实现逻辑，所以它没有被优化）

代码：

J1SIZE = 3
J2SIZE = 4

frontier = []
explored = []


def IsEmpty(array):
    result = False
    if len(array) == 0:
        result = True
    return result


#Fill up a jug
def fillJug(tempNode, jug):
    copyNode = tempNode
    copyNode = copyNode
    if jug == 1:
        copyNode[0] = J1SIZE
    elif jug == 2:
        copyNode[1] = J2SIZE
    print(copyNode)
    return copyNode

#Empty a jug
def emptyJug(tempNode, jug):
    copyNode = tempNode
    if jug == 1:
        copyNode[0] = 0
    elif jug == 2:
        copyNode[1] = 0
    print(copyNode)
    return copyNode

#Pass the content of a jug to another
def passJug(tempNode, jug):
    copyNode = tempNode
    if jug == 1:
        copyNode[1] = copyNode.j1
        copyNode[0] = 0
        if copyNode[1] > J2SIZE:
            copyNode[1] = J2SIZE
    elif jug == 2:
        copyNode[0] = copyNode[1]
        copyNode[1] = 0
        if copyNode[0] > J1SIZE:
            copyNode[0] = J1SIZE
    print(copyNode)
    return copyNode

#Check if solution was found
def goalTest(goalNode,currentNode):
    result = False
    if goalNode == currentNode:
        result = True
    return result

def BFS(start,end,frontier,explored):

    start_node = start
    frontier = [start_node] + frontier

    if goalTest(end,(frontier[0])):
        print('Solution:', frontier[0])
        exit()

    #Loop start
    while IsEmpty(frontier) == False:

        tempNode = frontier.pop(0)

        #Generate nodes (states)
        if tempNode[0] < J1SIZE:
            newNode = fillJug(tempNode, 1)
            if newNode not in explored:
                frontier = [newNode] + frontier
                print('Frontier1: ', frontier)

        if tempNode[1] < J2SIZE:
            newNode = fillJug(tempNode, 2)
            if newNode not in explored:
                frontier = [newNode] + frontier
                print('Frontier2: ', frontier)

        if tempNode[0] == J1SIZE:
            newNode = emptyJug(tempNode, 1)
            if newNode not in explored:
                frontier = [newNode] + frontier
                print('Frontier3: ', frontier)

        if tempNode[1] == J2SIZE:
            newNode = emptyJug(tempNode, 2)
            if newNode not in explored:
                frontier = [newNode] + frontier
                print('Frontier4: ', frontier)

        if (tempNode[0] > 0) and (tempNode[1] < J2SIZE):
            newNode = passJug(tempNode, 1)
            if newNode not in explored:
                frontier = [newNode] + frontier
                print('Frontier5: ', frontier)

        if (tempNode[1] > 0) and (tempNode[0] < J1SIZE):
            new_node = passJug(tempNode, 2)
            if new_node not in explored:
                frontier = [new_node] + frontier
                print('Frontier6: ', frontier)

        print('Frontier: ', frontier)
        print('Explored: ', explored)

        for node in frontier:
            if goalTest(end, node):
                print('Solution:', frontier[0])
                exit()
            if node not in explored:
                explored = [node] + explored

BFS([0,0],[0,2],frontier,explored)

固定代码：

http://codepaste.net/auun4u

Answer 1

我制作了一个较小的代码示例来重现您的错误：

J1SIZE = 3
J2SIZE = 4


def fillJug(tempNode, jug):
    copyNode = tempNode
    copyNode = copyNode
    if jug == 1:
        copyNode[0] = J1SIZE
    elif jug == 2:
        copyNode[1] = J2SIZE
    return copyNode


frontier = [[0, 0]]
tempNode = frontier.pop(0)

newNode = fillJug(tempNode, 1)
frontier = [newNode] + frontier  # (1)

newNode = fillJug(tempNode, 2)  # (2)
frontier = [newNode] + frontier

问题是，在我标记为(1)的行中，您设置了newNode，它将与tempNode相同的对象作为{{1}中的第一项}}。然后，在我标记为frontier的行中，您正在更改(2) - 在tempNode内。所以fillJug中的值会发生变化。具体来说，您frontier引用与copyNode相同的对象，然后您要更改tempNode（和copyNode）引用的数据。

您应该将tempNode重新定义为

copyNode

这将导致copyNode = tempNode[:]和copyNode引用内存中的不同对象（具有相同的值）。（另一种选择是在导入copy后将tempNode设置为copyNode。）

所以新的copy.copy(tempNode)将是

fillJug

同样的修复适用于其他def fillJug(tempNode, jug): copyNode = tempNode[:] if jug == 1: copyNode[0] = J1SIZE elif jug == 2: copyNode[1] = J2SIZE return copyNode函数。

即使列表未传递给函数，函数也会更改列表中的值

1 个答案: