Aeroplane chess HDU - 4405_数学期望_逆推

 

Code：

#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
const int maxn = 100000 + 233;
const double perc = (1 / 6.0);
double f[maxn];
int vis[maxn];
int main()
{
    int n,m;
    while(1)
    {
        memset(vis, -1, sizeof(vis));
        memset(f,0, sizeof(f));
        scanf("%d%d",&n,&m);
        if(!n) break;
        for(int i = 1;i <= m; ++i)
        {
            int a,b;
            scanf("%d%d",&a,&b);
            vis[a] = b;
        }
        for(int i = n - 1;i >= 0;--i)
        {
            if(vis[i] != -1){ f[i] = f[vis[i]] ;  continue; }
            for(int j = 1;j <= 6; ++j) f[i] += (f[i + j] + 1) * perc;
        }
        printf("%.4lf\n",f[0]);
    }
    return 0;
}