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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")