割顶点（或者称为关节点）

割顶点（或关节点）是指在无向连通图中，删除该顶点及其相关边后，会使得原图变为非连通图的顶点。下面是一个使用深度优先搜索（DFS）算法来找出割顶点的代码示例：

def articulation_points(graph):
    num_nodes = len(graph)
    visited = [False] * num_nodes
    parent = [-1] * num_nodes
    low = [float('inf')] * num_nodes
    discovery = [float('inf')] * num_nodes
    is_articulation = [False] * num_nodes
    time = 0

    def dfs(node, visited, parent, low, discovery, is_articulation):
        nonlocal time
        children = 0
        visited[node] = True
        discovery[node] = time
        low[node] = time
        time += 1

        for neighbor in graph[node]:
            if not visited[neighbor]:
                parent[neighbor] = node
                children += 1
                dfs(neighbor, visited, parent, low, discovery, is_articulation)
                low[node] = min(low[node], low[neighbor])

                if parent[node] == -1 and children > 1:
                    is_articulation[node] = True
                
                if parent[node] != -1 and low[neighbor] >= discovery[node]:
                    is_articulation[node] = True

            elif neighbor != parent[node]:
                low[node] = min(low[node], discovery[neighbor])

    for node in range(num_nodes):
        if not visited[node]:
            dfs(node, visited, parent, low, discovery, is_articulation)

    result = []
    for node in range(num_nodes):
        if is_articulation[node]:
            result.append(node)

    return result

该代码首先使用DFS遍历图中的每个连通分量，对于每个顶点，记录其发现时间（discovery）、最早可达祖先的发现时间（low）、访问状态（visited）、父节点（parent）和是否为割顶点（is_articulation）。在DFS遍历中，如果发现一个顶点是割顶点，则将is_articulation[node]置为True。最后，返回所有割顶点的列表。

使用示例：

graph = {
    0: [1, 2],
    1: [0, 2],
    2: [0, 1, 3, 5],
    3: [2, 4],
    4: [3],
    5: [2, 6, 8],
    6: [5, 7],
    7: [6, 8],
    8: [5, 7]
}

result = articulation_points(graph)
print(result)  # 输出：[2, 5]

在上述示例中，图中的割顶点为2和5。