HDU 4405 Aeroplane chess 概率dp

1.1667
2.3441 

模拟飞行棋

倒着推期望的时候要注意特判能直接飞的点

//做了五题概率dp了终于1A了 开心~

ACcode：

#include <iostream>
#include <cstdio>
#include <cstring>
#define maxn 100010
using namespace std;
double dp[maxn];
int from[maxn];
int to[maxn];
int main(){
    int n,m;
    while(scanf("%d%d",&n,&m),n|m){
        memset(from,0,sizeof(from));
        memset(dp,0,sizeof(dp));
        memset(to,0,sizeof(to));
        for(int i=0;i<m;++i){
            int x,y;
            scanf("%d%d",&x,&y);
            to[x]=y;
            from[y]=x;
        }
        for(int i=1;i<=n;++i){
                if(to[to[i]])to[i]=to[to[i]];
                if(from[from[i]])from[i]=from[from[i]];
        }
      //  for(int i=1;i<=n;++i)printf("to[%d] = %d      from[%d] = %d\n",i,to[i],i,from[i]);
        for(int i=n-1;i>=0;--i){
            double sum=0;
            double e=1.0/6;
            if(to[i]){
                dp[i]=dp[to[i]];
                continue;
            }
            for(int k=1;k<=6;++k)
                    sum+=dp[k+i]*e;
                    dp[i]=sum+1;
        }
        printf("%.4lf\n",dp[0]);
    }
    return 0;
}