hdu 4405 Aeroplane chess

http://acm.hdu.edu.cn/showproblem.php?pid=4405

代码：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#include <vector>
#include <algorithm>

#define LL long long
//#pragma comment(linker, "/STACK:1024000000,1024000000")
using namespace std;
const int N=100015;
double ans[N];
int f[N];
int main()
{
    //freopen("data.txt","r",stdin);
    int n,m;
    while(scanf("%d %d",&n,&m)!=EOF)
    {
        if(n==0&&m==0)
        break;
        memset(f,-1,sizeof(f));
        while(m--)
        {
            int i,j;
            scanf("%d %d",&i,&j);
            f[i]=j;
        }
        for(int i=0;i<=n+5;++i)
        ans[i]=0.0;
        for(int i=n-1;i>=0;--i)
        {
            if(f[i]!=-1)
            {
                ans[i]=ans[f[i]];
            }else
            {
                for(int j=i+1;j<=i+6;++j)
                {
                    ans[i]+=(ans[j]+1.0)/6.0;
                }
            }
        }
        printf("%.4lf\n",ans[0]);
    }
    return 0;
}