用python实现BFS -- 算法导论

代码如下：

color = {}
pi = {}
d = {}
G = {'S':('R','W'),
'W':('S','T', 'X'),
'R':('S','V'),
'V':('R'),
'T':('U','W', 'X'),
'X':('W','T', 'U', 'Y'),
'U':('T','X', 'Y'),
'Y':('X','V'),
}
def main():
BFS(G, 'S')
print(color)
print(pi)
print(d)
def BFS(G, s):

global color, pi, d, Q
for v in G:
color[v] = 'white'
pi[v] = 'NIL'
d[v] = float('inf')
color[s] = 'gray'
pi[s] = 'NIL'
d[s] =0
Q = 5*['0']
ENQUEUE(Q, s)
while(Qhead != Qtail):
u = DEQUEUE(Q)
for v in G[u]:
if color[v] == 'white':
color[v] = 'gray'
d[v] = d[u] + 1
pi[v] = u
ENQUEUE(Q, v)
color[u] = 'black'
def ENQUEUE(Q, x):
global Qtail
Q[Qtail] = x
if Qtail == len(Q) - 1:
Qtail = 0
else:
Qtail = Qtail + 1
def DEQUEUE(Q):
global Qhead
x = Q[Qhead]
if Qhead == len(Q) - 1:
Qhead = 0
else:
Qhead = Qhead + 1
return x

Qhead = 0

图示

算法导论（第三版）的BFS伪代码