模拟赛硬磕1h方差被方差了QwQ

#include<bits/stdc++.h>
using namespace std;
#define N 100005
#define ls rt<<1
#define rs rt<<1|1
struct node{
	int l,r,add;
	double sum,sf;
}tree[N<<2];
int n,m,a[N];
void push_up(int rt){ 
	tree[rt].sum=tree[ls].sum+tree[rs].sum;
	tree[rt].sf=tree[ls].sf+tree[rs].sf;
	return;
}
void build(int rt,int x,int y){ 
	tree[rt].l=x,tree[rt].r=y,tree[rt].add=0;
	if(x==y){
		tree[rt].sum=a[x];
		tree[rt].sf=a[x]*a[x];
		return;
	}
	int mid=(x+y)>>1;
	build(ls,x,mid);
	build(rs,mid+1,y);
	push_up(rt);
	return;
}
void push_down(int rt){ 
	if(tree[rt].add){
		tree[ls].add+=tree[rt].add;
		tree[rs].add+=tree[rt].add;
		tree[ls].sf+=tree[rt].add*tree[rt].add*(tree[ls].r-tree[ls].l+1)+2*tree[rt].add*tree[ls].sum;
		tree[rs].sf+=tree[rt].add*tree[rt].add*(tree[rs].r-tree[rs].l+1)+2*tree[rt].add*tree[rs].sum;
		tree[ls].sum+=tree[rt].add*(tree[ls].r-tree[ls].l+1);
		tree[rs].sum+=tree[rt].add*(tree[rs].r-tree[rs].l+1);
		tree[rt].add=0;
	}
	return;
}
void update(int rt,int x,int y,int z){
	if(x<=tree[rt].l&&tree[rt].r<=y){
		tree[rt].sf+=2*z*tree[rt].sum+(tree[rt].r-tree[rt].l+1)*z*z;
		tree[rt].sum+=z*(tree[rt].r-tree[rt].l+1);
		tree[rt].add+=z;
		return;
	}
	push_down(rt);
	int mid=(tree[rt].l+tree[rt].r)>>1;
	if(x<=mid) update(ls,x,y,z);
	if(y>mid) update(rs,x,y,z);
	push_up(rt);
	return;
}
double query1(int rt,int x,int y){
	if(x<=tree[rt].l&&y>=tree[rt].r) return tree[rt].sum;
	push_down(rt);
	double ret=0;
	int mid=(tree[rt].l+tree[rt].r)>>1;
	if(x<=mid) ret+=query1(ls,x,y);
	if(y>mid) ret+=query1(rs,x,y);
	push_up(rt);
	return ret;
}
double query2(int rt,int x,int y){
	if(x<=tree[rt].l&&y>=tree[rt].r) return tree[rt].sf;
	push_down(rt);
	double ret=0;
	int mid=(tree[rt].l+tree[rt].r)>>1;
	if(x<=mid) ret+=query2(ls,x,y);
	if(y>mid) ret+=query2(rs,x,y);
	push_up(rt);
	return ret;
}
signed main() {
	ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
	cin>>n>>m;
	for(int i=1;i<=n;i++) cin>>a[i];
	build(1,1,n);
	for(int i=1;i<=m;i++){
		int opt,x,y,k;
		cin>>opt>>x>>y;
		if(opt==1){
			cin>>k;
			update(1,x,y,k);
		}
		else if(opt==2) printf("%.4lf\n",query1(1,x,y)/(y-x+1));
		else{
			double q=query1(1,x,y)/(y-x+1);
			printf("%.4lf\n",query2(1,x,y)/n-q*q);
		}
	}
	return 0;
}