用adjacency list实现的BFS。
用2个list储存状态：先初始化color，把所有点设为0，即还没遍历。然后把遍历过的点标成1；第二个List，Q，作用是deque（先进先出），把正在遍历的点，比如点1，push进deque，然后把与1相邻的点再push进deque。然后再把1从deque，即Q中删除。
def graph_BFS(G,s):
inf = 1e8
color = []
Q = []
count = 0
n = len(G)
for v in range(0,n):
color.append(0)
Q.append(s)
count = count + 1
color[s] = 1
while(Q!=[]):
temp = Q[0]
print temp
#下面是把color不为1的graph[count - 1]里的item放进Q
if(count-1<n):
for i in G[count-1]:
if(color[i] == 0):
Q.append(i)
Q.remove(temp)
count = count + 1
#放进Q里的item变颜色
for v in Q:
color[v] = 1
graph = [[1,2,3],[5],[],[4],[5],[]]
graph1 = [[1],[2,3,4],[3,4],[],[]]
graph2 = [[1,2],[3],[0,4,5],[],[2,5,7],[2,4,7,6],[5,7],[4,5,6]]
source = 0
graph_BFS(graph2,source)
[github代码地址]https://github.com/will-I-amor/python/blob/master/BFS.py
