Particle accelerator

input/code.cpp: In function 'll min_energy(vi)':
input/code.cpp:32:34: warning: comparison of integer expressions of different signedness: 'll' {aka 'long long int'} and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   32 | #define loop(n) for (ll i = 0; i < n; i++)
      |                                  ^
input/code.cpp:47:3: note: in expansion of macro 'loop'
   47 |   loop(particles.size() - 1) {
      |   ^~~~

#include <bits/stdc++.h>
using namespace std;
// clang-format off
template<typename A, typename B> ostream& operator<<(ostream &os, const pair<A, B> &p) { return os << '(' << p.first << ", " << p.second << ')'; }
template<typename T_container, typename T = typename enable_if<!is_same<T_container, string>::value, typename T_container::value_type>::type> ostream& operator<<(ostream &os, const T_container &v) { os << '{'; string sep; for (const T &x : v) os << sep << x, sep = ", "; return os << '}'; }
void dbg_out() { cerr << endl; }
template<typename Head, typename... Tail> void dbg_out(Head H, Tail... T) { cerr << ' ' << H; dbg_out(T...); }
template <typename T> istream &operator>>(istream &is, vector<T> &v) { T value; is >> value; v.push_back(value); return is; }
#define preamble ios::sync_with_stdio(0); cin.tie(0); dbg("INIT");
// clang-format on
#ifdef DO_DBG
#define dbg(...) cerr << "(" << #__VA_ARGS__ << "):", dbg_out(__VA_ARGS__)
#else
#define dbg(...)
#endif
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef vector<ll> vi;
typedef vector<bool> vb;
typedef set<ll> si;
typedef pair<ll, ll> pi;
typedef vector<pair<ll, ll>> vpi;
#define F first
#define S second
#define PB push_back
#define MP make_pair
const int MAX_N = 1e5 + 5;
const ll MOD = 1e9 + 7;
const ll INF = 1e9;
const ld EPS = 1e-9;
#define loop(n) for (ll i = 0; i < n; i++)
#define loopi(n, i) for (ll i = 0; i < n; i++)
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define sq(x) (x * x)

ll n;
vi a;

ll min_energy(vi particles) {
  if (particles.size() == 2) {
    auto p1 = particles[0], p2 = particles[1];
    return p1 * p2 - sq(min(p1, p2));
  }
  ll best = INF;
  loop(particles.size() - 1) {
    auto part2 = particles;
    auto p1 = part2[i];
    auto p2 = part2[i + 1];
    part2.erase(part2.begin() + i);
    part2.erase(part2.begin() + i);
    part2.insert(part2.begin() + i, p1 + p2);
    auto res = min_energy(part2) + p1 * p2 - sq(min(p1, p2));
    dbg(particles, part2, res);
    best = min(best, res);
  }
  return best;
}

int main() {
  preamble;
  cin >> n;
  loop(n) cin >> a;
  dbg(n, a);
  cout << min_energy(a) << "\n";
}

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: WRONG ANSWER

Test 7

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Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: WRONG ANSWER

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: WRONG ANSWER

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: WRONG ANSWER

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Verdict: ACCEPTED

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Test 20

Verdict: ACCEPTED

Test 21

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Test 22

Verdict: ACCEPTED

Test 23

Verdict: ACCEPTED

Test 24

Verdict: WRONG ANSWER

Test 25

Verdict: ACCEPTED

Test 26

Verdict: ACCEPTED

Test 27

Verdict: WRONG ANSWER

Test 28

Verdict: ACCEPTED

Test 29

Verdict: WRONG ANSWER

Test 30

Verdict: ACCEPTED

Test 31

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