HDU 1596 find the safest road

#include <iostream>
#include <string>
using namespace std;
const double esp=1e-11;
const int maxn=1001;
int n;
double Map[maxn][maxn];
double dis[maxn];
int vis[maxn];
double Dijkstra(int s,int t)
{
memset(vis,0,sizeof(vis));
memset(dis,0,sizeof(dis));
dis[s]=1;
for(int i=0;i<n;i++)
{
int u;
double ans=-1;
for(int j=1;j<=n;j++)
if(!vis[j] && dis[j]>ans)
{
ans=dis[j];
u=j;
}
vis[u]=1;
if(u==t)return ans;
for(int j=1;j<=n;j++)
if(!vis[j] && dis[j]<Map[u][j]*dis[u])
dis[j]=Map[u][j]*dis[u];
}
}
int main()
{
while(~scanf("%d",&n))
{
for(int i=1;i<=n;i++)
for(int j=1;j<=n;j++)
scanf("%lf",&Map[i][j]);
for(int i=1;i<=n;i++)
for(int j=1;j<=n;j++)
if(Map[i][j]>1-esp&&Map[i][j]<1+esp)
Map[i][j]=0;
int m,s,t;
scanf("%d",&m);
while(m--)
{
scanf("%d%d",&s,&t);
double ans=Dijkstra(s,t);
if(ans)
printf("%.3lf\n",ans);
else
puts("What a pity!");
}
}
return 0;
}