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;

}