leetcode 802 find eventual safe states

class (object):
    def eventualSafeNodes(self, graph):
        """
        :type graph: List[List[int]]
        :rtype: List[int]
        """
        if not graph: return []

        n = len(graph)
        
        d = {u:[] for u in range(n)}
        degree = [0] * n
        for u in range(n):
            for v in graph[u]:
                d[v].append(u)
            degree[u] = len(graph[u])

        Q = [u for u in range(n) if degree[u]==0]
        res = []
        while Q:
            node = Q.pop()
            res.append(node)
            for nodes in d[node]:
                degree[nodes] -= 1
                if degree[nodes] == 0:
                    Q.append(nodes)
        return sorted(res)