Segment Tree - find maxsum between a[x] -> a[y]

#include <bits/stdc++.h>
using namespace std;
const long long N = 5e4, lim = -1e9;
struct T
{
    long long prefix, sum, suffix, best;
};
T Tree[4*N+1];
long long n, m, a[N+1];
T Connect(const T & u, const T & v)
{
    T last;
    last.sum = u.sum + v.sum;
    last.prefix = max(u.prefix, u.sum + v.prefix);
    last.suffix = max(v.suffix, v.sum + u.suffix);
    last.best = max(u.best, max(v.best, u.suffix + v.prefix));
    return last;
}
void BuildTree(int id, int TreeL, int TreeR)
{
    if (TreeL == TreeR)
    {
        Tree[id].prefix = Tree[id].sum = Tree[id].suffix = Tree[id].best = a[TreeL];
        return ;
    }
    int mid = (TreeL + TreeR)/2;
    BuildTree(id * 2, TreeL, mid);
    BuildTree(id * 2 + 1, mid + 1, TreeR);
    Tree[id] = Connect(Tree[id * 2], Tree[id * 2 + 1]);
}
T Get(int id, int TreeL, int TreeR, int l, int r)
{
    if (l > r)
    {
        return {0, lim, lim, lim};
    }
    if (l == TreeL && r == TreeR)
    {
        return Tree[id];
    }
    int mid = (TreeL + TreeR)/2;
    return Connect(Get(id * 2, TreeL, mid, l, min(mid, r)), Get(id * 2 + 1, mid + 1, TreeR, max(l, mid + 1), r));
}
void read()
{
    cin >> n;
    for (long long i = 1; i <= n; ++ i)
    {
        cin >> a[i];
    }
    BuildTree(1, 1, n);
}
void solve()
{
    cin >> m;
    long long x, y;
    while (m--)
    {
        cin >> x >> y;
        cout << Get(1, 1, n, x, y).best << '\n';
    }
}
int main()
{
   ios_base::sync_with_stdio(false);
   cin.tie(nullptr);
   //freopen(task".INP", "r", stdin);
   //freopen(task".OUT", "w", stdout);
   long long t = 1;
   bool typetest = false;
   if (typetest)
   {
      cin >> t;
   }
   for (long long __ = 1; __ <= t; ++ __)
   {
      read();
      solve();
   }
}