AC日记——方差 洛谷 P1471

方差

思路：

　　线段树；

代码：

#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*+size*x*x;
        sum+=x*size;
    }
};
struct TreeNodeType tree[maxn<<];
int n,m;
double X,Sum,Sum2;
inline void in(int &now)
{
    int if_z=;now=;
    char Cget=getchar();
    while(Cget>''||Cget<'')
    {
        if(Cget=='-') if_z=-;
        Cget=getchar();
    }
    while(Cget>=''&&Cget<='')
    {
        now=now*+Cget-'';
        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+;
    if(l==r)
    {
        scanf("%lf",&tree[now].sum);
        tree[now].sum2=tree[now].sum*tree[now].sum;
        return;
    }
    tree[now].mid=l+r>>;
    build(now<<,l,tree[now].mid);
    build(now<<|,tree[now].mid+,r);
    tree[now].sum=tree[now<<].sum+tree[now<<|].sum;
    tree[now].sum2=tree[now<<].sum2+tree[now<<|].sum2;
}
inline void pushdown(int now)
{
    tree[now<<].updata(tree[now].flag);
    tree[now<<|].updata(tree[now].flag);
    tree[now].flag=;
}
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<<,l,r);
    if(r>tree[now].mid) operation1(now<<|,l,r);
    tree[now].sum=tree[now<<].sum+tree[now<<|].sum;
    tree[now].sum2=tree[now<<].sum2+tree[now<<|].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<<,l,r);
    if(r>tree[now].mid) operation2(now<<|,l,r);
}
int main()
{
    in(n),in(m),build(,,n);
    int op,l,r;
    while(m--)
    {
        in(op),in(l),in(r);
        if(op==) scanf("%lf",&X),operation1(,l,r);
        if(op==) Sum=,operation2(,l,r),printf("%.4lf\n",Sum/(r-l+));
        if(op==)
        {
            Sum=,Sum2=;
            operation2(,l,r);
            X=Sum/(r-l+);
            printf("%.4lf\n",(Sum2-Sum*X*+(r-l+)*X*X)/(r-l+));
        }
    }
    return ;
}