从文件中读取有向图

Question

大家好——如果有人想知道，我是编码新手。

这是我第一次在这里发帖，我目前正忙于我的一项任务。下面的代码是我的草稿代码。

adjacency_list 的预期输出是：

[[1,3], [2], [3], [0,2]]
# with possibly [3,1] instead of [1,3] or [0,2] instead of [2,0]

我的代码的输出是：

[[1, 3], [2], [3], [0, 2]]——这就是我想要的

对于maximal_path 的预期输出是：

[0, 1, 2, 3] 和 [0, 3, 2]

而我的输出是：

[0, 1, 3, 2] - 这与我的教授想要的预期输出完全不同。我一直在经历第二个功能并不断陷入死胡同。谁能告诉我第二个功能的错误在哪里？

这里是 digraph.txt 列表：

6 4
0 1
0 3
1 2
2 3
3 0
3 2

-

谢谢！

def adjacency_list(file_name):

    # create empty list
    adj_temp_list = []

    # open input file
    f = open('digraph0.txt','r')

    # read first line
    in_file = f.readline()

    first_row = [int(i) for i in in_file.strip().split()]

    # first_row[0] represents number of edges and first_row[1] represents number of vertices

    # add number of vertices amount of empty lists to adj_temp_list
    for i in range(first_row[1]):

        adj_temp_list.append([])

    # read edges( each line represents one edge)
    for i in range(first_row[0]):
        line = f.readline()

        # split the line and convert the returned list into a list of integers
        vertex=[int(i) for i in line.strip().split()]

        # vertex[0] and vertex[1] represents start vertex and end vertex respectively.
        # that is, vertex[1] is adjacent vertex or neighbour to vertex[0]
        # Thus, append vertex[1] to the adjcency list of vertex[0]

        adj_temp_list[vertex[0]].append(vertex[1])

    # close input file
    f.close()

    # create a new empty list
    adj_list=[]

    # sort each list in the adj_temp_list and append to adj_list
    for lst in adj_temp_list:
        lst.sort()
        adj_list.append(lst)

    # return the adjacency list
    return adj_list

def maximal_path(file_name,start):

    # call adjacency_list function to get adjacency list
    adj_list=adjacency_list(file_name)

    # create max_path as an empty list
    max_path=[]

    # create a boolean list that represents which vertex is added to path
    # Thus, initialize the list such that it represents no vertex is added to path
    visited=[False]*len(adj_list)

    # create an empty list(stack)
    stack=[]

    # add start vertex to stack list
    stack.append(start)

    # process until there is no possibility to extend the path
    while True:

    # get a node u from stack and remove it from stack
        u=stack[0]
        stack=stack[1:]

    # set vertex u visited and add it to max_path
        visited[u]=True
        max_path.append(u)

    # find whether u has unvisited neighbours to extend path or not
        existNeighbour=False
        for v in adj_list[u]:
            if visited[v]==False:
                existNeighbour=True
                break

    # if u has unvisited adjacent vertices
        if existNeighbour==True:

        # push all un-visited neighbours into stack
            for v in adj_list[u]:
                stack.append(v)

    # if u has no unvisited adjacent vertices, exit the loop
        else:
            break

# return the maximal path
    return max_path

Answer 1

您的方法就是所谓的Breadth First Search 或 BFS。当您将新节点附加到堆栈的末尾时，将逐层探索图形。为了获得预期的输出，您可以对程序进行的最小更改是在堆栈的开头插入新节点。

stack.insert(0,v)