从 0 到各点各要几步

七个点，走不到的记成 -1。运行下面这段程序：

from collections import deque

def dist(g, s):
    d = {s: 0}
    q = deque([s])
    while q:
        u = q.popleft()
        for v in g[u]:
            if v not in d:
                d[v] = d[u] + 1
                q.append(v)
    return [d.get(i, -1) for i in sorted(g)]

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 dist(g, 0)))