这里做一下记录，不是想要讲解什么，怕以后自己会忘记，所以写的很粗糙，但是我别的blog还是很用心的。哈哈
大家共勉~~~
import random
from time import time
NUM_MC_ROUNDS = 100 # 可修改
class SimuGreedy:
def __init__(self):
with open("graph.txt", "r") as file:
self.graph = [[float(x) for x in line.split()] for line in file]
self.num_vert = len(self.graph)
self.status = [0 for _ in range(self.num_vert)]
self.seed_set = []
print('Graph with {0} vertices has been loaded.'.format(self.num_vert))
print('Number of rounds in single Monte Carlo simulation: {0}'.format(NUM_MC_ROUNDS))
def get_seed_set(self):
tic = time()
while True:
max_val = max_id = 0
for idx, state in enumerate(self.status):
if state == 0:
# print('evaluating V{0}'.format(idx))
val = self.simulate_influence(idx)
# print('V{0}: {0}'.format(idx, val))
if val > max_val:
max_val = val
max_id = idx
self.seed_set.append(max_id)
self.status[max_id] = 1
# if max_val >= self.num_vert:
if len(self.seed_set) == 5:
break
else:
print('Current expected #influenced: {0}, {1}-element seed set: {2}'.format(
max_val, len(self.seed_set), self.seed_set
))
return self.seed_set, time() - tic
def simulate_influence(self, vert_id):
test_seed_set = [seed for seed in self.seed_set]
test_seed_set.append(vert_id)
cnt = 0
for _ in range(NUM_MC_ROUNDS):
live_set = [seed for seed in test_seed_set]
newly_influenced_set = []
temp_status = [s for s in self.status]
temp_status[vert_id] = 1
cnt += len(test_seed_set)
while True:
for idx, state in enumerate(temp_status):
if state == 0:
prob_not_influenced = 1.
for live in live_set:
prob_not_influenced *= 1 - self.graph[live][idx]
prob_influenced = 1 - prob_not_influenced
if prob_influenced >= self.get_rand():
temp_status[idx] = 1
newly_influenced_set.append(idx)
if len(newly_influenced_set) == 0:
break
cnt += len(newly_influenced_set)
live_set = [inf for inf in newly_influenced_set]
newly_influenced_set = []
return cnt / NUM_MC_ROUNDS
@staticmethod
def get_rand():
return random.uniform(0, 1)
if __name__ == '__main__':
seed_set, time_cost = SimuGreedy().get_seed_set()
print('--------------')
print('Time cost: {0} s'.format(time_cost))
print('Final indexes of vertices in {0}-element seed set:'.format(len(seed_set)))
print(seed_set)
