概率dp
#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5+7;
int n,m;
vector<int> G[maxn];
int deg[maxn];
double dp1[maxn],dp2[maxn];
double topsort1(int x)
{
if(x==n) return 0;
if(dp1[x]) return dp1[x];
double sum = 0;
for(int i=0;i<G[x].size();i++)
{
int v = G[x][i];
sum += topsort1(v);
}
return dp1[x] = sum/deg[x]+1.0+1.0/deg[x];
}
double topsort2(int x)
{
if(x==n) return 0;
if(dp2[x]) return dp2[x];
double sum = 0;
for(int i=0;i<G[x].size();i++)
{
int v = G[x][i];
sum += topsort2(v);
}
return dp2[x] = sum/deg[x]+dp1[x]+dp1[x]/deg[x];
}
int main()
{
int T;
scanf("%d",&T);
while(T--)
{
memset(G,0,sizeof(G));
memset(deg,0,sizeof(deg));
memset(dp1,0,sizeof(dp1));
memset(dp2,0,sizeof(dp2));
scanf("%d%d",&n,&m);
for(int i=0;i<m;i++)
{
int u,v;
scanf("%d%d",&u,&v);
G[u].push_back(v);
deg[u]++;
}
topsort1(1);
printf("%.2lf\n",topsort2(1));
}
return 0;
}