Method dfs

python/2092-find-all-people-with-secret.py:12–18

(src, adj)

            time_map[t][dst].append(src)
        
        def dfs(src, adj):
            if src in visit:
                return
            visit.add(src)
            secrets.add(src)
            for nei in adj[src]:
                dfs(nei, adj)

        for t in sorted(time_map.keys()):
            visit = set()