DFS 从 0 出发的访问顺序

七个点的图，邻居表都按编号从小到大排好。运行下面这段程序：

def dfs(g, s):
    seen = set()
    out = []
    def go(u):
        seen.add(u)
        out.append(u)
        for v in g[u]:
            if v not in seen:
                go(v)
    go(s)
    return out

g = {0: [1, 2], 1: [0, 3], 2: [0, 4],
     3: [1, 4], 4: [2, 3], 5: [6], 6: [5]}
print("/".join(str(x) for x in dfs(g, 0)))