AC日记——方差 洛谷 P1471

#include <bits/stdc++.h>
using namespace std;
#define maxn 100005
struct TreeNodeType {
    int l,r,mid,size;
    double sum,sum2,flag;
    inline void updata(double x)
    {
        flag+=x;
        sum2+=sum*x*2+size*x*x;
        sum+=x*size;
    }
};
struct TreeNodeType tree[maxn<<2];
int n,m;
double X,Sum,Sum2;
inline void in(int &now)
{
    int if_z=1;now=0;
    char Cget=getchar();
    while(Cget>‘9‘||Cget<‘0‘)
    {
        if(Cget==‘-‘) if_z=-1;
        Cget=getchar();
    }
    while(Cget>=‘0‘&&Cget<=‘9‘)
    {
        now=now*10+Cget-‘0‘;
        Cget=getchar();
    }
    now*=if_z;
}
void build(int now,int l,int r)
{
    tree[now].l=l,tree[now].r=r,tree[now].size=r-l+1;
    if(l==r)
    {
        scanf("%lf",&tree[now].sum);
        tree[now].sum2=tree[now].sum*tree[now].sum;
        return;
    }
    tree[now].mid=l+r>>1;
    build(now<<1,l,tree[now].mid);
    build(now<<1|1,tree[now].mid+1,r);
    tree[now].sum=tree[now<<1].sum+tree[now<<1|1].sum;
    tree[now].sum2=tree[now<<1].sum2+tree[now<<1|1].sum2;
}    
inline void pushdown(int now)
{
    tree[now<<1].updata(tree[now].flag);
    tree[now<<1|1].updata(tree[now].flag);
    tree[now].flag=0;
}
void operation1(int now,int l,int r)
{
    if(tree[now].l>=l&&tree[now].r<=r)
    {
        tree[now].updata(X);
        return;
    }
    if(tree[now].flag) pushdown(now);
    if(l<=tree[now].mid) operation1(now<<1,l,r);
    if(r>tree[now].mid) operation1(now<<1|1,l,r);
    tree[now].sum=tree[now<<1].sum+tree[now<<1|1].sum;
    tree[now].sum2=tree[now<<1].sum2+tree[now<<1|1].sum2;
}
void operation2(int now,int l,int r)
{
    if(tree[now].l>=l&&tree[now].r<=r)
    {
        Sum+=tree[now].sum;
        Sum2+=tree[now].sum2;
        return;
    }
    if(tree[now].flag) pushdown(now);
    if(l<=tree[now].mid) operation2(now<<1,l,r);
    if(r>tree[now].mid) operation2(now<<1|1,l,r);
}
int main()
{
    in(n),in(m),build(1,1,n);
    int op,l,r;
    while(m--)
    {
        in(op),in(l),in(r);
        if(op==1) scanf("%lf",&X),operation1(1,l,r);
        if(op==2) Sum=0,operation2(1,l,r),printf("%.4lf\n",Sum/(r-l+1));
        if(op==3)
        {
            Sum=0,Sum2=0;
            operation2(1,l,r);
            X=Sum/(r-l+1);
            printf("%.4lf\n",(Sum2-Sum*X*2+(r-l+1)*X*X)/(r-l+1));
        }
    }
    return 0;
}