使用 BFS 查找从开始到结束节点的所有路径答案

【问题标题】：Find all paths from start to end node using BFS使用 BFS 查找从开始到结束节点的所有路径
【发布时间】：2020-11-03 16:26:57
【问题描述】：

使用下面的 BFS 实现，我们如何修改程序以存储从开始到结束节点的所有路径？有什么想法吗？

def bfs(graph_to_search, start, end):
    queue = [[start]]
    visited = set()

    while queue:
        # Gets the first path in the queue
        path = queue.pop(0)

        # Gets the last node in the path
        vertex = path[-1]

        # Checks if we got to the end
        if vertex == end:
            return path
        # We check if the current node is already in the visited nodes set in order not to recheck it
        elif vertex not in visited:
            # enumerate all adjacent nodes, construct a new path and push it into the queue
            for current_neighbour in graph_to_search.get(vertex, []):
                new_path = list(path)
                new_path.append(current_neighbour)
                queue.append(new_path)

            # Mark the vertex as visited
            visited.add(vertex)

【问题讨论】：

标签： python python-3.x data-structures breadth-first-search

【解决方案1】：

也许这样的事情可以奏效。我认为在检查节点是否被访问时，您将从结果中排除许多路径，仅仅是因为它们包含相同的节点。我将其更改为添加访问的整个路径，并改为检查。还创建了一个空列表results，如果找到最终节点，我们将附加到该列表中。您的代码将在找到最后一个节点的那一刻从函数返回，并且不会探索并找到剩余的路径。让我知道这是否有效！

def bfs(graph_to_search, start, end):
    queue = [[start]]
    visited = set()
    results = []

    while queue:
        # Gets the first path in the queue
        path = queue.pop(0)

        # Gets the last node in the path
        vertex = path[-1]

        # Checks if we got to the end
        if vertex == end:
            results.append(path)
            continue
        # We check if the current path is already in the visited nodes set in order not to recheck it
        elif path not in visited:
            # enumerate all adjacent nodes, construct a new path and push it into the queue
            for current_neighbour in graph_to_search.get(vertex, []):
                new_path = path.copy()
                new_path.append(current_neighbour)
                queue.append(new_path)

            # Mark the vertex as visited
            visited.add(path)
      return results

您还可以将queue 中的元素保存为包含当前顶点和上一个路径的元组，就像这样。可能更具可读性。

queue = [(start, [])]
vertex, path = queue.pop(0)

【讨论】：