广度优先搜索

代码：

import collectionsdef bfs(G,s):    P,Q={s:None},collections.deque([s])    while Q:        u=Q.popleft()        for v in G[u]:            if v in P:continue            P[v]=u            Q.append(v)    return Pif __name__=="__main__":    a, b, c, d, e, f, g, h, i= range(9)    N = [        {b, c, d}, # a        {a, d}, # b        {a,d}, # c        {a,b,c}, # d        {g,f}, # e        {e,g}, # f        {e,f}, # g        {i}, # h        {h} #i    ]    G=[{b,c,d,e,f},#a     {c,e},#b     {d},#c     {e},#d     {f},#e     {c,g,h},#f     {f,h},#g     {f,g}#h     ]    p=bfs(G,0)

运行：

>>> p{0: None, 1: 0, 2: 0, 3: 0, 4: 0, 5: 0, 6: 5, 7: 5}

寻找从a到u的路径的话，只需要在返回的队列中“往回倒”就好了。

>>> u=6>>> path =[u]>>> while p[u] is not None:path.append(p[u])u=p[u]>>> path.reverse()>>> >>> path[0, 5, 6]