Please Help Me ! why my code is giving wrong answer

problem:

#include<bits/stdc++.h>
#define fast ios_base::sync_with_stdio(false);cin.tie(0);
#define lli long long int
#define vi vector<lli>
#define pb push_back
#include<string>
#define mp map<string,lli>
#define ss set<lli>
#define MOD 1000000007
#define test lli t;cin>>t;while(t--)
using namespace std;
int main()
{
    test
    {
        lli n;
        cin>>n;
        vi arr(n),brr(n);
        for(auto &it:arr)
            cin>>it;
        for(auto &it:brr)
            cin>>it;
        vi a(n,0),b(n,0);
        a[0]=arr[0];
        b[0]=brr[0];
        for(lli i=1;i<n;i++)
            a[i]=arr[i]+a[i-1];
        for(lli i=1;i<n;i++)
            b[i]=brr[i]+b[i-1];
        if(a[n-1]>b[n-1])
            cout<<a[n-1]<<endl;
        else if(a[n-1]<b[n-1])
            cout<<b[n-1]<<endl;
        else
        {
            lli x=-1;
            for(lli i=0;i<n;i++)
            {
                if(a[i]>b[i])
                {
                    x=i;
                    break;
                }
            }
            lli sum=a[x];
            for(lli j=x+1;j<n;j++)
                sum+=brr[j];
            if(x==-1)
                cout<<a[n-1]<<endl;
            else
            cout<<sum<<endl;
        }
    }
}