cf 283A

不能简单模拟（会超时）  运用一点小技巧  减少时间复杂度

#include <cstdio>
#include <cstring>
 
using namespace std;
int a[200010];
int cc[200010];
int main()
{
    int t,n,m,tt;
    scanf("%d",&t);
    memset(cc, 0, sizeof(cc));
    memset(a, 0 ,sizeof(a));
    int top = 1;
    double sum = 0;
    while(t--)
    {
        scanf("%d",&tt);
        if(tt == 1)
        {
            scanf("%d%d",&n,&m);
            cc[n] += m;
            sum += n*m;
        }
        else if(tt == 2)
        {
            scanf("%d",&n);
            a[++top] = n;
            sum += n;
        }
        else
        {
            cc[top-1] += cc[top];
            sum -= (a[top]+cc[top]);
            cc[top] = 0;
            top--;
        }
        printf("%.6lf\n",sum/top);
    }
}