POJ 3259 Wormholes【Bellman_ford判断负环】

 1 #include<iostream>  
 2 #include<cstdio>  
 3 #include<cstring> 
 4 #include <cmath> 
 5 #include<stack>
 6 #include<vector>
 7 #include<map> 
 8 #include<set>
 9 #include<queue> 
10 #include<algorithm>  
11 using namespace std;
12 
13 typedef long long LL;
14 const int INF = (1<<30)-1;
15 const int maxn=10005;
16 int d[maxn];
17 int flag;
18 int nodenum,edgenum,ecnt;
19 
20 struct Edge{
21     int u,v,cost;
22 } e[maxn];
23 
24 int Bellman_ford(){
25     for(int i=1;i<=nodenum;i++) d[i]=INF;
26     d[1]=0;
27     
28     for(int i=1;i<nodenum;i++){
29         for(int j=1;j<=ecnt;j++){
30             if(d[e[j].v]>d[e[j].u]+e[j].cost)
31             d[e[j].v]=d[e[j].u]+e[j].cost;
32         }
33     }
34     
35     flag=1;
36     for(int i=1;i<=ecnt;i++){
37         if(d[e[i].v]>d[e[i].u]+e[i].cost){
38             flag=0;
39             break;
40         }
41     }
42     return flag;    
43 }
44 
45 void addedges(int a,int b,int c){
46     e[++ecnt].u=a;
47     e[ecnt].v=b;
48     e[ecnt].cost=c;    
49 }
50 
51 int main(){
52     int m,w,ncase;
53     int a,b,c;
54     scanf("%d",&ncase);
55     while(ncase--){
56         ecnt=0;
57         scanf("%d %d %d",&nodenum,&m,&w);
58         while(m--){
59             scanf("%d %d %d",&a,&b,&c);
60             addedges(a,b,c);
61             addedges(b,a,c);            
62         }
63         while(w--){
64             scanf("%d %d %d",&a,&b,&c);
65             c=-c;
66             addedges(a,b,c);
67         }
68         if(Bellman_ford()) printf("NO\n");
69         else printf("YES\n");    
70     }
71     return 0;
72 }