~题目链接~
http://poj.org/problem?id=1860
Sample Input
3 2 1 20.0 1 2 1.00 1.00 1.00 1.00 2 3 1.10 1.00 1.10 1.00
Sample Output
YES
1.Spfa
1 #include<stdio.h> 2 #include<string.h> 3 #include<stdlib.h> 4 #include<queue> 5 #define maxn 2<<28 6 #define maxm 1000+10 7 8 using namespace std; 9 10 struct node 11 { 12 double x,y; 13 } map[maxm][maxm]; 14 15 double dis[maxm]; 16 queue<int>Q; 17 18 int Spfa(int n,int s,double k) 19 { 20 while(!Q.empty()) 21 Q.pop(); 22 int flag[maxm],i; 23 memset(flag,0,sizeof(flag)); 24 for(i=1; i<=n; i++) 25 dis[i]=maxn; 26 Q.push(s); 27 dis[s]=k; 28 flag[s]=1; 29 while(!Q.empty()) 30 { 31 int h=Q.front(); 32 Q.pop(); 33 flag[h]=0; 34 for(i=1; i<=n; i++) 35 if(dis[i]<(dis[h]-map[h][i].y)*map[h][i].x)//松弛 36 { 37 dis[i]=(dis[h]-map[h][i].y)*map[h][i].x; 38 if(!flag[i]) 39 { 40 Q.push(i); 41 flag[i]=1; 42 } 43 } 44 if(dis[s]>k)//判断是否存在正环 45 return 1; 46 } 47 return 0; 48 } 49 50 int main() 51 { 52 int n,m,s,a,b,i; 53 double k,u,v,w,z; 54 while(~scanf("%d%d%d%lf",&n,&m,&s,&k)) 55 { 56 for(i=0; i<m; i++) 57 { 58 scanf("%d%d%lf%lf%lf%lf",&a,&b,&u,&v,&w,&z); 59 map[a][b].x=u; 60 map[a][b].y=v; 61 map[b][a].x=w; 62 map[b][a].y=z; 63 } 64 if(Spfa(n,s,k)) 65 printf("YES "); 66 else 67 printf("NO "); 68 } 69 return 0; 70 }
2.Bellman_ford
1 #include<stdio.h> 2 #include<string.h> 3 #include<stdlib.h> 4 #define maxm 1000+10 5 6 struct node 7 { 8 int u,v; 9 double x,y; 10 } map[maxm]; 11 12 double dis[maxm]; 13 int num; 14 15 int Bellman_ford(int n,int s,double k) 16 { 17 int i,j,flag; 18 memset(dis,0,sizeof(dis)); 19 dis[s]=k; 20 for(i=0; i<n; i++) 21 { 22 flag=0; 23 for(j=1; j<=num; j++) 24 if(dis[map[j].v]<(dis[map[j].u]-map[j].y)*map[j].x) 25 { 26 dis[map[j].v]=(dis[map[j].u]-map[j].y)*map[j].x; 27 flag=1; 28 } 29 if(!flag) 30 break; 31 } 32 if(i>=n)//判断松弛后，是否存在正环 33 return 1; 34 return 0; 35 } 36 37 int main() 38 { 39 int n,m,s,a,b,i; 40 double k,u,v,w,z; 41 while(~scanf("%d%d%d%lf",&n,&m,&s,&k)) 42 { 43 num=0; 44 for(i=0; i<m; i++) 45 { 46 scanf("%d%d%lf%lf%lf%lf",&a,&b,&u,&v,&w,&z); 47 map[++num]=((struct node){a,b,u,v}); 48 map[++num]=((struct node){b,a,w,z}); 49 } 50 if(Bellman_ford(n,s,k)) 51 printf("YES "); 52 else 53 printf("NO "); 54 } 55 return 0; 56 }