Revise paste Untitled

#include <iostream>
#include <vector>
#include <queue>
#include <cstring>
#include <algorithm>
#include <fstream>
using namespace std;
const int maxn = 1e6 + 5;
int segment_tree[3 * maxn];
void build_tree(int L, int R, int position) {
    if(L == R) {
        segment_tree[position] = 0;
    }
    else {
        int middle = (L + R) / 2;
        build_tree(L, middle, 2 * position);
        build_tree(middle + 1, R, 2 * position + 1);
        segment_tree[position] = segment_tree[2 * position] + segment_tree[2 * position + 1];
    }
}
int query(int L, int R, int position, int i, int j) {
    // L R i L R j L R
    if(i <= L and R <= j) {
        return segment_tree[position];
    }
    if(L > j or R < i) {
        return 0;
    }
    int middle = (L + R) / 2;
    return query(L, middle, 2 * position, i, j) + query(middle + 1, R, 2 * position + 1, i, j);
}
void update(int L, int R, int position, int idx) {
    if(L == R) {
        segment_tree[position] = 1;
        return;
    }
    int middle = (L + R) / 2;
    if(idx <= middle) {
        update(L, middle, 2 * position, idx);
    }
    else {
        update(middle + 1, R, 2 * position + 1, idx);
    }
    segment_tree[position] = segment_tree[2 * position] + segment_tree[2 * position + 1];
}
int main() {
    ios_base::sync_with_stdio(false);
    int n;
    cin >> n;
    
    vector<int> v(n);
    for(int i = 0; i < n; i++) {
        cin >> v[i];
    }
    build_tree(0, n, 1);
    long long result = 0;
    for(int i = n - 1; i >= 0; i--) {
        update(0, n, 1, v[i]);
        result += query(0, n, 1, 0, v[i] - 1);
    }
    cout << result << endl;
    return 0;
}