POJ3259 Wormholes —— spfa求负环

  1 #include <iostream>
  2 #include <cstdio>
  3 #include <cstring>
  4 #include <algorithm>
  5 #include <vector>
  6 #include <cmath>
  7 #include <queue>
  8 #include <stack>
  9 #include <map>
 10 #include <string>
 11 #include <set>
 12 #define rep(i,a,n) for(int (i) = a; (i)<=(n); (i)++)
 13 #define ms(a,b) memset((a),(b),sizeof((a)))
 14 using namespace std;
 15 typedef long long LL;
 16 const double EPS = 1e-8;
 17 const int INF = 2e9;
 18 const LL LNF = 9e18;
 19 const int MOD = 1e9+7;
 20 const int MAXN = 1e3+10;
 21 
 22 int N, M, W;
 23 
 24 struct edge
 25 {
 26     int to, w, next;
 27 }edge[MAXN*MAXN];
 28 int cnt, head[MAXN];
 29 
 30 void add(int u, int v, int w)
 31 {
 32     edge[cnt].to = v;
 33     edge[cnt].w = w;
 34     edge[cnt].next = head[u];
 35     head[u] = cnt++;
 36 }
 37 
 38 void init()
 39 {
 40     cnt = 0;
 41     memset(head, -1, sizeof(head));
 42 }
 43 
 44 int dis[MAXN], times[MAXN], inq[MAXN];
 45 bool spfa(int st)
 46 {
 47     memset(inq, 0, sizeof(inq));
 48     memset(times, 0, sizeof(times));
 49     for(int i = 1; i<=N; i++)
 50         dis[i] = INF;
 51 
 52     queue<int>Q;
 53     Q.push(st);
 54     inq[st] = 1;
 55     dis[st] = 0;
 56     while(!Q.empty())
 57     {
 58         int u = Q.front();
 59         Q.pop(); inq[u] = 0;
 60         for(int i = head[u]; i!=-1; i = edge[i].next)
 61         {
 62             int v = edge[i].to;
 63             if(dis[v]>dis[u]+edge[i].w)
 64             {
 65                 dis[v] = dis[u]+edge[i].w;
 66                 if(!inq[v])
 67                 {
 68                     Q.push(v);
 69                     inq[v] = 1;
 70                     if(++times[v]>N) return true;
 71                 }
 72             }
 73         }
 74     }
 75     return false;
 76 }
 77 
 78 int main()
 79 {
 80     int T;
 81     scanf("%d",&T);
 82     while(T--)
 83     {
 84         init();
 85         scanf("%d%d%d", &N, &M, &W);
 86         for(int i = 1; i<=M; i++)
 87         {
 88             int s, e, t;
 89             scanf("%d%d%d", &s, &e, &t);
 90             add(s, e, t);
 91             add(e, s, t);
 92         }
 93 
 94         for(int i = 1; i<=W; i++)
 95         {
 96             int s, e, t;
 97             scanf("%d%d%d", &s, &e, &t);
 98             add(s, e, -t);
 99         }
100 
101         int flag = 0;
102         for(int i = 1; i<=N; i++)
103         if(spfa(i)) 
104         {
105             flag = 1;
106             break;
107         }
108         
109 
110         if(flag)
111             puts("YES");
112         else
113             puts("NO");
114     }
115 }