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904. 虫洞
题意
思路
代码
904. 虫洞
题意
见原题
思路
看是否有负环即可
别忘把所有点都入队
代码
''' Author: NEFU AB-IN Date: 2022-04-16 16:17:22 FilePath: \ACM\Acwing\904.py LastEditTime: 2022-04-16 16:17:23 '''
from collections import deque
N = 550
INF = int(1e9)
g = [[] for _ in range(N)]
dist, st, cnt = [INF] * N, [0] * N, [0] * N
def spfa():
q = deque()
for i in range(1, n + 1):
q.appendleft(i)
st[i] = 1
dist[i] = 0
while q:
u = q.pop()
st[u] = 0
for v, w in g[u]:
if dist[v] > dist[u] + w:
dist[v] = dist[u] + w
if st[v] == 0:
st[v] = 1
q.appendleft(v)
cnt[v] = cnt[u] + 1
if cnt[v] >= n:
return 1
return 0
for _ in range(int(input())):
g = [[] for _ in range(N)]
dist, st, cnt = [INF] * N, [0] * N, [0] * N
n, m, w = map(int, input().split())
for i in range(m):
u, v, t = map(int, input().split())
g[u].append([v, t])
g[v].append([u, t])
for i in range(w):
u, v, t = map(int, input().split())
g[u].append([v, -t])
if spfa():
print("YES")
else:
print("NO")
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