直接邻居和能走到的，差多少

七个点的图，0 号的邻居表是 [1, 2]。运行下面这段程序，看它的直接邻居有几个、一路能走到几个：

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(str(len(g[0])) + "/" + str(len(dfs(g, 0))))