Secomd max using SEGment tree

#include "bits/stdc++.h"
using namespace std;
#define ll long long int
#define rep(i,a,n)  for(int i = a; i < n; i++)
#define A(v)  (v.begin(), v.end())
#define S(x)    scanf("%I64d", &x)
#define s(x)   scanf("%d", &x)
#define pb(x)   push_back(x)
#define V       vector < int >
const int N =  4e5+5;
vector < int > ans1, ans2;
bool al, ar;
struct st{
    int x, y;
}tree[N];
int arr[N];
void build(int l, int r, int node){
    if(l == r){
        tree[node].x = arr[l];
        tree[node].y = 0;
        return;
    }
    int mid = (l+r) >> 1, lc = node + node;
    build(l, mid, lc);
    build(mid + 1, r, lc | 1);
    vector < int > a;
    a.pb(tree[lc].x),a.pb(tree[lc].y),a.pb(tree[lc|1].x),a.pb(tree[lc|1].y);
    sort(a.begin(), a.end());
    tree[node].x = a.back(); tree[node].y = a[2];
}
void query(int l, int r, int ql, int qr, int node, bool a){
    if(qr < l or ql > r)return ;
   /* if(l == r and (l == ql || l == qr)){
            if(l == ql)al = true;
            else ar = true;
            return 0;//return tree[node].x;
    }
   // if(l == r){ans.pb(arr[l]);return 0;}
   // if(a and ql <= l and r <= qr)return tree[node].y;
   // if(!a and ql <= l and r <= qr)return tree[node].x;*/
   if(a and ql <= l and r <= qr){
        ans1.pb(tree[node].y);
        ans1.pb(tree[node].x);
        return;
   }

    int mid = (l+r) >> 1, lc = node + node;
    query(l, mid, ql, qr, lc, a), query(mid + 1, r, ql, qr, lc|1, a);
}
void upd(int l, int r, int pos, int val, int node){
    if(pos < l or pos > r)return;
    if(l == r){
        tree[node].x = val;
        tree[node].y = 0;
        arr[l] = val;
        return ;
    }
   // if(ql <= l and )

    int mid = (l+r) >> 1, lc = node + node;
    upd(l, mid, pos, val, lc);
    upd(mid + 1, r, pos, val, lc|1);
    vector < int > a;
    a.pb(tree[lc].x),a.pb(tree[lc].y),a.pb(tree[lc|1].x),a.pb(tree[lc|1].y);
    sort(a.begin(), a.end());
    tree[node].x = a.back(); tree[node].y = a[2];
}

int main(){
    ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
    int n, i, j, k, l, r, q, x, y;char ch;
    cin >> n;
    for(i = 1; i <= n; i++)cin >> arr[i];
    build(1, n, 1);
    //cout << query(1, n, 1, 4, 1, 0) << ' ' << query(1, n, 1, 4, 1, 1) << '\n';
    cin >> q;

    while(q--){
            ans1.clear();al = 0, ar = 0;//ans2.clear();
            //scanf("%c %d %d", ch, &l, &r);
           cin >> ch >> l >> r;
       //cout << l << ' ' << r << '\n';
     //  cout << ch << '\n';
    if(ch == 'U'){upd(1, n, l, r, 1);continue;}
   // cout << query(1, n, l, r, 1, 0) << ' ' << query(1, n, l, r, 1, 1) << '\n';
   // if(r <= n){
     //(query(1, n, l, r, 1, 0)) ;
      (query(1, n, l, r, 1,1));
    sort(ans1.begin(),ans1.end());

    cout << ans1.back() +  ans1[ans1.size()-2] << '\n';
    //printf("%d\n", x + y);
   // }
    }
   // rep(i,1,4*n)if(tree[i].x)cout << i << ' ' << tree[i].x << ' ' << tree[i].y << '\n';
    return 0;
}