数学专项counting：UVa 10081

#include <iostream>
#include <fstream>
#include <cstring>
#include <cstdio>
#include <cmath>
using namespace std;
int n,k;
double dp[110][12];
int vis[110][12];
double dfs(int dep,int i)
{
if(vis[dep][i]) return dp[dep][i];
if(dep==n) return dp[dep][i]=1;
vis[dep][i]=1;
double &ans=dp[dep][i];
ans=dfs(dep+1,i);
if(i>0) ans+=dfs(dep+1,i-1);
if(i<k) ans+=dfs(dep+1,i+1);
return ans;
}
int main()
{
freopen("in.txt","r",stdin);
while(cin>>k>>n)
{
memset(vis,0,sizeof(vis));
double ans=0;
for(int i=0;i<=k;i++)
ans+=dfs(1,i);
printf("%.5f\n",ans*100/pow((k+1)*1.0,n));
}
return 0;
}