Segtree2.cpp

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;

template <class T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

#define int long long int
#define pb push_back
#define pi pair<int, int>
#define pii pair<int, pi>
#define fir first
#define sec second
#define MAXN 500001
#define mod 1000000007

struct segtree
{
  int n;
  vector<int> seg;

  int neutral()
  {
    return 0;
  }
  int merge(int a, int b)
  {
    return a + b;
  }
  void build(vector<int> &v)
  {
    n = 1;
    while (n < v.size())
      n <<= 1;
    seg.assign(n << 1, neutral());
    for (int i = 0; i < v.size(); i++)
      seg[i + n] = v[i];
    for (int i = n - 1; i; i--)
      seg[i] = merge(seg[i << 1], seg[(i << 1) | 1]);
  }
  void upd(int i, int value)
  {
    seg[i] = merge(seg[i += n], value);
    for (i >>= 1; i; i >>= 1)
      seg[i] = merge(seg[i << 1], seg[(i << 1) | 1]);
  }
  int qry(int l, int r)
  {
    int ansl = neutral(), ansr = neutral();
    for (l += n, r += n + 1; l < r; l >>= 1, r >>= 1)
    {
      if (l & 1)
        ansl = merge(ansl, seg[l++]);
      if (r & 1)
        ansr = merge(seg[--r], ansr);
    }
    return merge(ansl, ansr);
  }
};
signed main()
{
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  return 0;
}
// iterative segtree without lazy propagation