BFS 从 0 出发的访问顺序

同一张图，这次用队列一圈一圈扩。运行下面这段程序：

from collections import deque

def bfs(g, s):
    seen = {s}
    q = deque([s])
    out = []
    while q:
        u = q.popleft()
        out.append(u)
        for v in g[u]:
            if v not in seen:
                seen.add(v)
                q.append(v)
    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 bfs(g, 0)))