路径查找器代码，__getitem__ TypeError

Question

我正在尝试做一个“路径查找器”

def find_all_paths(start, end, graph, path=[]):
    path = path + [start]
    if start == end:
        return [path]
    paths = []
    for node in graph[start]:
        if node not in path:
            newpaths = find_all_paths(graph, node, end, path)
            for newpath in newpaths:
                paths.append(newpath)
    return paths


 graph={1: ['2'], 2: ['3', '4', '5'], 3: ['4'], 4: ['5', '6'], 5: [], 6: []}

如果我在 shell 中输入 find_all_paths(2,5,graph) 我应该取回从图形字典中的键 2 到 5 值的所有路径 一个正确的结果应该是这样的

path=[[2,5],[2,3,4,5][2,4,5]]

代码不断给出值错误，例如

   for node in graph[start]:
TypeError: 'int' object has no attribute '__getitem__'

有人可以帮我把这个东西运行起来

Answer 1

有几个尴尬和错误：

不要使用列表初始化 path 参数，而是使用None。 并在函数体中创建空列表。

def find_all_paths(start, end, graph, path=None):
    path = path or []

传递给find_all_paths 的值不尊重签名。 改为这样写：

newpaths = find_all_paths(node, end, graph, path)

由于值是整数，因此图表必须包含 int 而不是 strings。

graph = {1: [2], 2: [3, 4, 5], 3: [4], 4: [5, 6], 5: [], 6: []}

这是您的代码的固定版本：

def find_all_paths(start, end, graph, path=None):
    path = path or []
    path.append(start)
    if start == end:
        return [path]
    paths = []
    for node in graph[start]:
        if node not in path:
            newpaths = find_all_paths(node, end, graph, path)
            for newpath in newpaths:
                paths.append(newpath)
    return paths

如果你试试这个：

graph = {1: [2], 2: [3, 4, 5], 3: [4], 4: [5, 6], 5: [], 6: []}
print(find_all_paths(2, 5, graph))

你会得到：

[[2, 3, 4, 5, 6]]