python实现拓扑排序的方法步骤

 1  →  2  →  4
 ↓  ↗ ↓  ↗ ↓
 3    5  →  6

from collections import defaultdict, deque

def topological_sort(graph):
    # 统计入度
    indegree = defaultdict(int)
    for node in graph:
        for neighbor in graph[node]:
            indegree[neighbor] += 1
    
    # 将入度为0的节点加入队列
    queue = deque([node for node in graph if indegree[node] == 0])
    result = []
    
    # 拓扑排序
    while queue:
        node = queue.popleft()
        result.append(node)
        # 将该节点的邻接节点的入度减1，并将入度为0的节点加入队列
        for neighbor in graph[node]:
            indegree[neighbor] -= 1
            if indegree[neighbor] == 0:
                queue.append(neighbor)
    
    # 如果结果中的节点数等于图中的节点数，则拓扑排序成功
    if len(result) == len(graph):
        return result
    else:
        return None

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

sorted_nodes = topological_sort(graph)
if sorted_nodes:
    print("拓扑排序结果:", sorted_nodes)
else:
    print("图中存在环，无法进行拓扑排序")