【期望DP】HDU4405 Aeroplane chess

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;

const int maxn=100010;
int n,m,to[maxn];
double f[maxn];
int main(){
scanf("%d%d",&n,&m);
while (n){
for (int i=0;i<=n;i++) to[i]=i;
for (int i=1,x,y;i<=m;i++) scanf("%d%d",&x,&y),to[x]=y;
memset(f,0,sizeof(f));
for (int i=n-1;i>=0;i--){
if (to[i]>i) {f[i]=f[to[i]];continue;}
f[i]=1;
for (int j=1;j<=6;j++)
f[i]+=f[i+j]/6;
}
printf("%.4lf\n",f[0]);
scanf("%d%d",&n,&m);
}
return 0;
}