Problem p03514 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
#define ll long long
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define rrep(i, n) for (int i = (int)(n)-1; i >= 0; --i)
#define srep(i, s, t) for (int i = (int)(s); i < (int)(t); ++i)
#define each(a, b) for (auto(a) : (b))
#define all(v) (v).begin(), (v).end()
#define len(v) (int)(v).size()
#define zip(v) sort(all(v)), v.erase(unique(all(v)), v.end())
#define cmx(x, y) x = max(x, y)
#define cmn(x, y) x = min(x, y)
#define fi first
#define se second
#define pb push_back
#define show(x) cout << #x << " = " << (x) << endl
#define spair(p) cout << #p << ": " << p.fi << " " << p.se << endl
#define svec(v)                                                                \\
  cout << #v << ":";                                                           \\
  rep(kbrni, v.size()) cout << " " << v[kbrni];                                \\
  cout << endl
#define sset(s)                                                                \\
  cout << #s << ":";                                                           \\
  each(kbrni, s) cout << " " << kbrni;                                         \\
  cout << endl
#define smap(m)                                                                \\
  cout << #m << ":";                                                           \\
  each(kbrni, m) cout << " {" << kbrni.first << ":" << kbrni.second << "}";    \\
  cout << endl

using namespace std;

typedef pair<int, int> P;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<double> vd;
typedef vector<P> vp;
typedef vector<string> vs;

const int MAX_N = 100005;

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  vd p(2 * n);
  rep(i, 2 * n) { cin >> p[i]; }
  sort(all(p), greater<ll>());
  double ans = 0;
  srep(i, 1, 2 * n + 1) { ans += p[i - 1] * (2 * n - i) / (2 * n - 1); }
  printf("%.10f\\n", ans);
  return 0;
}


Error: WA

Fixed submission:

#include <bits/stdc++.h>
#define ll long long
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define rrep(i, n) for (int i = (int)(n)-1; i >= 0; --i)
#define srep(i, s, t) for (int i = (int)(s); i < (int)(t); ++i)
#define each(a, b) for (auto(a) : (b))
#define all(v) (v).begin(), (v).end()
#define len(v) (int)(v).size()
#define zip(v) sort(all(v)), v.erase(unique(all(v)), v.end())
#define cmx(x, y) x = max(x, y)
#define cmn(x, y) x = min(x, y)
#define fi first
#define se second
#define pb push_back
#define show(x) cout << #x << " = " << (x) << endl
#define spair(p) cout << #p << ": " << p.fi << " " << p.se << endl
#define svec(v)                                                                \\
  cout << #v << ":";                                                           \\
  rep(kbrni, v.size()) cout << " " << v[kbrni];                                \\
  cout << endl
#define sset(s)                                                                \\
  cout << #s << ":";                                                           \\
  each(kbrni, s) cout << " " << kbrni;                                         \\
  cout << endl
#define smap(m)                                                                \\
  cout << #m << ":";                                                           \\
  each(kbrni, m) cout << " {" << kbrni.first << ":" << kbrni.second << "}";    \\
  cout << endl

using namespace std;

typedef pair<int, int> P;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<double> vd;
typedef vector<P> vp;
typedef vector<string> vs;

const int MAX_N = 100005;

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  vl p(n);
  rep(i, 2 * n) { cin >> p[i]; }
  sort(all(p));
  double ans = 0;
  vector<double> val(n);
  val[1] = 1;
  srep(i, 1, n + 1) {
    ans += p[i - 1] * val[i];
    val[i + 1] = val[i] * (2 * n - 2 * i) / (2 * n - 2 * i + 1);
  }
  srep(i, n + 1, 2 * n + 1) { ans += p[i - 1] * (1.0 - val[2 * n + 1 - i]); }
  printf("%.12lf\\n", ans);
  return 0;
}