HDU-1596-find the safest road

HDU-1596-find the safest road

http://acm.hdu.edu.cn/showproblem.php?pid=1596

SPFA演算法

#include<iostream>#include<cstdio>#include<cstring>using namespace std;int n,m,st,ed,front,rear;double mat[1005][1005],dis[1005];int v[1005],q[1000001]; void spfa(){int i,p;while(front<rear){p=q[front++];v[p]=0;for(i=0;i<n;i++){if(mat[p][i]==0||p==i)continue;if(dis[p]*mat[p][i]>dis[i]){dis[i]=dis[p]*mat[p][i];if(!v[i]){q[rear++]=i;v[i]=1;}}}}}int main(){int i,j;while(scanf("%d",&n)!=EOF){for(i=0;i<n;i++)for(j=0;j<n;j++)scanf("%lf",&mat[i][j]);scanf("%d",&m);while(m--){scanf("%d%d",&st,&ed);memset(v,0,sizeof(v));memset(dis,0,sizeof(dis));v[st-1]=1;dis[st-1]=1;front=0;rear=1;q[front]=st-1;spfa();if(dis[ed-1]!=0)printf("%.3lf\n",dis[ed-1]);elseprintf("What a pity!\n");}}return 0;}