codeforces 808B

题意：给定一组数，每k个长度求一次和，求平均值

#include<cstdio>#include<algorithm>using namespace std;int a[2*100001];int main(){int n,k;//freopen("in.txt","r",stdin);while(~scanf("%d%d",&n,&k)){int num=n-k+1;double sum=0;double ans=0;for(int i=1;i<=n;i++){scanf("%d",&a[i]);sum+=a[i];if(i>=k){sum-=a[i-k];ans+=sum;}}ans/=num;printf("%.12lf\n",ans);}}