func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     ios_base::sync_with_stdio(0);     cin.tie();     int n;     cin >> n;     vector<pair<int, int> > arr[1001];     for (int i = 1; i <= n; i++) {       int x, y;       cin >> x >> y;       arr[x / 1000].push_back(make_pair(y, i));     }     for (int i = 0; i < 1001; i++)       if (arr[i].size() > 1) sort(arr[i].begin(), arr[i].end());     bool flag = 0;     for (int i = 0; i < 1001; i++) {       if (arr[i].size()) {         flag = (!flag);         if (flag)           for (int j = 0; j < arr[i].size(); j++) cout << arr[i][j].second <<    ;         else           for (int j = arr[i].size() - 1; j >= 0; j--)             cout << arr[i][j].second <<    ;       }     }   }   