rt,萌新刚学线段树，WA on #1,2,3,4,8,9,求调 val1区间和，val2区间平方和，query直接返回区间和。

#include<iostream>
#include<iomanip>
using namespace std;

#define N 100005
#define D double

D n,m,op,x,y,t,a[N];

struct node{
	int l,r;
	D val1,val2,tag;
}seg[4*N];

bool in(int L,int R,int nl,int nr){
	return L>=nl&&R<=nr;
}

bool out(int L,int R,int nl,int nr){
	return L>nr||R<nl;
}

void mtag(int u,int nl,int nr,D t){
	seg[u].val2+=t*t*(nr-nl+1)+2*t*seg[u].val1;
	seg[u].tag+=t,seg[u].val1+=(nr-nl+1)*t;
}

void pushdown(int u,int nl,int nr){
	int mid=(nl+nr)/2;
	mtag(u*2,nl,mid,seg[u].tag);
	mtag(u*2+1,mid+1,nr,seg[u].tag);
	seg[u].tag=0;
}
void pushup(int u){
	seg[u].val1=seg[u*2].val1+seg[u*2+1].val1;
	seg[u].val2=seg[u*2].val2+seg[u*2+1].val2;
}

D query1(int typ,int u,int nl,int nr,int L,int R){
	if(in(nl,nr,L,R)){
		if(typ==1) return seg[u].val1;
		else return seg[u].val2;
	}
	else if(!out(nl,nr,L,R)){
		pushdown(u,nl,nr);
		int mid=(nl+nr)/2;
		return query1(typ,u*2,nl,mid,L,R)+query1(typ,u*2+1,mid+1,nr,L,R);
	}
	else return 0;
}

D query2(int x,int y){
	D a1=query1(2,1,1,n,x,y);
	D a2=(D)query1(1,1,1,n,x,y)/(D)(y-x+1);
	return (a1+a2*a2*n-2*a2*query1(1,1,1,n,x,y))/(D)(y-x+1);
}

void update(int u,int nl,int nr,int L,int R,D t){
	if(in(nl,nr,L,R)) mtag(u,nl,nr,t);
	else if(!out(nl,nr,L,R)){
		pushdown(u,nl,nr);
		int mid=(nl+nr)/2;
		update(u*2,nl,mid,L,R,t),update(u*2+1,mid+1,nr,L,R,t);
		pushup(u);
	}
}

void build(int u,int nl,int nr){
	
	seg[u].l=nl,seg[u].r=nr,seg[u].tag=0;
	if(nl==nr){
	    seg[u].val1=a[nl],seg[u].val2=a[nl]*a[nl];
		return;
	}
	int mid=(nl+nr)/2;
	build(u*2,nl,mid),build(u*2+1,mid+1,nr);
	pushup(u);
}
signed main(){
	
	cin>>n>>m;
	for(int i=1;i<=n;i++) cin>>a[i];
	build(1,1,n);
	
	while(m--){
		cin>>op>>x>>y;
		if(op==1) cin>>t,update(1,1,n,x,y,t);
		else if(op==2) cout<<setprecision(4)<<fixed<<(D)query1(1,1,1,n,x,y)/(D)(y-x+1)<<endl;
		else cout<<setprecision(4)<<fixed<<query2(x,y)<<endl;
	}
	return 0;
}