题目

#include<bits/stdc++.h>
#define int long long
using namespace std;
int n,l,r,a[100010],m,q[100010],ans;
signed main(){
	cin>>n;
	for(int i=1;i<=n;i++) cin>>a[i];
	cin>>m;
	l=m; r=m+n-1;
	for(int i=l;i<=r;i++) q[i]=a[i-m+1];
	for(int i=1;i<=m;i++){
		int x,y;
		cin>>x;
		if(x==1){
			if(r-l>0) r--;
		}
		else if(x==2){
			cin>>y;
			q[++r]=y;
		}
		else if(x==3){
			if(r-l>0) l++;
		}
		else if(x==4){
			cin>>y;
			q[--l]=y;
		}
	}
	for(int i=l;i<=r;i++){
		ans+=q[i];
	}
	cout<<ans;
	return 0;
	}