Concentric Tubes

#include <algorithm>
#include <iostream>
#include <vector>
typedef long long ll;

struct Tube {
  ll in;
  ll out;
  int idx;
};


int main(){
  int n;
  std::cin >> n;
  std::vector<Tube> tubes(n);
  for (int i = 0; i<n; ++i){
    tubes[i].idx = i+1;
    std::cin >> tubes[i].in;
  }
  for (int i = 0; i<n; ++i){
    std::cin >> tubes[i].out;
  }
  
  auto cmp = [](Tube& a, Tube& b){
    return a.in < b.in;
  };

  std::sort(tubes.begin(), tubes.end(), cmp);

  int i = n-1;
  std::vector<Tube> ans;
  ans.push_back(tubes[i]);
  --i;
  while(i>=0){
    if (tubes[i].out <= ans[ans.size()-1].in){
      ans.push_back(tubes[i]);
    }
    --i;
  }


  std::cout << ans.size() << "\n";
  for (int i = ans.size() - 1; i>=0; --i){
    std::cout << ans[i].idx << " ";
  }
  std::cout << "\n";

  
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED