hdu4405 掷骰子走格子

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

从0开始每次掷骰子，数字+骰子的数目，还有一种方式，直接乘给定的航班到某个更大编号的点，问数字大于等于N所需要的期望。

和poj2096一样，从d[>=n]推到d[0]，航班的处理是有则一定乘航班

#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<vector>
#include<algorithm>
#include<functional>
#include<iostream>
#include<cmath>
#include<string>
#include<cctype>
#include<stack>
#include<queue>
#include<set>
#include<sstream>
#include<map>
#include<ctime>
using namespace std;
#define For(i,k,n) for(int i=k;i<=n;i++)
#define ForD(i,k,n) for(int i=n;i>=k;i--)
#define Lson (x<<1)
#define Rson ((x<<1)+1)
#define MEM(a) memset(a,0,sizeof(a));
#define NEG(a) memset(a,-1,sizeof(a));
#define FILL(a) memset(a,0x3f,sizeof(a));
#define INF 0x3f3f3f3f
#define LLINF 0x3f3f3f3f3f3f3f3f
#define ll long long
#define print(b,a) cout<<b<<"="<<a<<endl;
#define printbin(b,a){int tmp=a;string s;do{s+=tmp%2+'0';tmp/=2;}while(tmp);reverse(s.begin(),s.end());cout<<"bin "<<b<<"="<<s<<endl;}
#define printarr(i,a,f,b) {For(i,f,b) printf("%d ",a[i]); printf("\n");}
#define fp   freopen("in.txt","r",stdin)
#define mod 1000000007


double d[200000];
int   mp[200000];
int main()
{
    int N,M;
    while(scanf("%d %d",&N,&M)&&!(N==0&&M==0))
    {
        For(i,N,100000+100)
        {
            d[i]=0;
        }
        NEG(mp);
        For(i,1,M) 
        {
            int u,v;
            scanf("%d %d",&u,&v);
            mp[u]=v;
        }
        ForD(i,0,N-1)
        {
            d[i]=1;
            For(k,1,6)
            {
                d[i]+=1.0/6*d[i+k];
            }
            if(mp[i]!=-1)
                d[i]=d[mp[i]];
            //printf("d[%d]=%lf\n",i,d[i]);
        }
        printf("%.4lf\n",d[0]);
    }
    return 0;
}