HDU-1596 find the safest road

/*
* hdu-1596	find the safest road
* mike-w
* 2011-8-25
* ---------------------
* AC 1000+ms
*/
#include<stdio.h>
#define SIZE 1111

int n,m;
double s[SIZE][SIZE];
double dist[SIZE];
int in[SIZE];

int extract(void)
{
int i,t;

for(i=1;i<=n;i++)
if(!in[i]&&dist[i]>-9999.0)
break;
for(t=i++;i<=n;i++)
if(!in[i]&&dist[i]>dist[t])
t=i;
return t>n?-1:t;
}

double dij(int e1,int e2)
{
int i,max;

for(i=1;i<=n;i++)
dist[i]=-9999.0,in[i]=0;
dist[e1]=1.0;
while((max=extract())!=e2)
{
if(max==-1)
return -1.0;
in[max]=1;
for(i=1;i<=n;i++)
if(!in[i]&&s[max][i]>0.0&&dist[max]*s[max][i]>dist[i])
dist[i]=dist[max]*s[max][i];
}
return dist[e2];
}

int main(void)
{
int i,j,t1,t2;
double t3;

#ifndef ONLINE_JUDGE
freopen("1596.in","r",stdin);
#endif

while(scanf("%d",&n)!=EOF)
{
for(i=1;i<=n;i++)
for(j=1;j<=n;j++)
scanf("%lf",s[i]+j);
scanf("%d",&m);
while(m-->0)
{
scanf("%d%d",&t1,&t2);
if((t3=dij(t1,t2))>0)
printf("%.3lf\n",t3);
else
puts("What a pity!");
}
}
return 0;
}