BIT - Gemp

#include <bits/stdc++.h>
using namespace std;
const int MAX = 300000;

int n, q, BIT[MAX], arr[MAX];

int query(int x) {
   int s = 0;
   while(x) s += BIT[x], x -= x&-x;
   return s;
}
void update(int x, int value) {
   while(x <= n) BIT[x] += value, x += x&-x;
}

int32_t main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

   cin >> n;
   for(int i = 1; i <= n; i++) {
      cin >> arr[i];
      update(i, arr[i]);
   }
   cin >> q;
   while(q--) {
      int o, a, b;
      cin >> o >> a >> b;
      if(o == 1) {
         cout << query(b) - query(a - 1) << endl;
      } else {
         update(a, -arr[a]);
         arr[a] = b;
         update(a, arr[a]);
      }
   }
    return 0;
}