主要找正环：
1 #include<cstdio> 2 #include<cstring> 3 #include<cstdlib> 4 #include<algorithm> 5 #include<iostream> 6 #include<queue> 7 #define MAXN 52000 8 using namespace std; 9 const int INF=-1<<28; 10 bool vis[MAXN]; 11 int head[MAXN]; 12 int next[MAXN]; 13 int s; 14 double dis[MAXN]; 15 struct node 16 { 17 int u,v; 18 double r,c; 19 }p[MAXN]; 20 int e,n,m; 21 int cnt[MAXN]; 22 double v; 23 void addnode(int u,int v,double r,double c) 24 { 25 p[e].u=u; 26 p[e].v=v; 27 p[e].r=r; 28 p[e].c=c; 29 next[e]=head[u]; 30 head[u]=e++; 31 } 32 bool relax(int u,int v,double r,double c) 33 { 34 if(dis[v]<(dis[u]-c)*r) 35 { 36 dis[v]=(dis[u]-c)*r; 37 return true; 38 } 39 return false; 40 } 41 bool spfa(int rc) 42 { 43 memset(vis,false,sizeof(vis)); 44 memset(cnt,0,sizeof(cnt)); 45 for(int i=1;i<=n;i++) 46 dis[i]=0; 47 dis[rc]=v; 48 vis[rc]=true; 49 queue<int>q; 50 q.push(rc); 51 ++cnt[rc]; 52 while(!q.empty()){ 53 int pre=q.front(); 54 q.pop(); 55 vis[pre]=false; 56 for(int i=head[pre];i+1;i=next[i]) 57 { 58 if(relax(pre,p[i].v,p[i].r,p[i].c)&&!vis[p[i].v]){ 59 if((++cnt[p[i].v])>n) return false; 60 q.push(p[i].v); 61 vis[p[i].v]=true; 62 } 63 } 64 } 65 return true; 66 } 67 int main() 68 { 69 memset(head, -1, sizeof(head)); 70 memset(next, -1, sizeof(next)); 71 e=0; 72 int a,b; 73 double r1,c1,r2,c2; 74 scanf("%d%d%d%lf",&n,&m,&s,&v); 75 for(int i=0;i<m;i++){ 76 scanf("%d%d%lf%lf%lf%lf",&a,&b,&r1,&c1,&r2,&c2); 77 addnode(a,b,r1,c1); 78 addnode(b,a,r2,c2); 79 } 80 if(!spfa(s)) printf("YES "); 81 else printf("NO "); 82 return 0; 83 } 84 85 86