Problem p01848 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>

#define _overload(_1, _2, _3, name, ...) name
#define _rep(i, n) _range(i, 0, n)
#define _range(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rep(...) _overload(__VA_ARGS__, _range, _rep, )(__VA_ARGS__)

#define _rrep(i, n) _rrange(i, n, 0)
#define _rrange(i, a, b) for (int i = (int)(a)-1; i >= (int)(b); --i)
#define rrep(...) _overload(__VA_ARGS__, _rrange, _rrep, )(__VA_ARGS__)

#define _all(arg) begin(arg), end(arg)
#define uniq(arg) sort(_all(arg)), (arg).erase(unique(_all(arg)), end(arg))
#define getidx(ary, key) lower_bound(_all(ary), key) - begin(ary)
#define clr(a, b) memset((a), (b), sizeof(a))
#define bit(n) (1LL << (n))

// #define DEBUG

#ifdef DEBUG
#define dump(...) fprintf(stderr, __VA_ARGS__)
#else
#define dump(...)
#endif

template <class T> bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T> bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}

using namespace std;
using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;

const double EPS = 1e-10;
const double PI = acos(-1.0);
const ll inf = 1LL << 62;
const ll mod = 1000000007LL;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

ll extgcd(ll a, ll b, ll &x, ll &y) {
  x = 1, y = 0;
  ll g = a;
  if (b != 0)
    g = extgcd(b, a % b, y, x), y -= a / b * x;
  return g;
}
ll ADD(const ll &a, const ll &b, const ll &mod) { return (a + b) % mod; }
ll SUB(const ll &a, const ll &b, const ll &mod) { return (a - b + mod) % mod; }
ll MUL(const ll &a, const ll &b, const ll &mod) { return (1LL * a * b) % mod; }
ll DIV(const ll &a, const ll &b, const ll &mod) {
  ll x, y;
  extgcd(b, mod, x, y);
  return MUL(a, (x + mod) % mod, mod);
}

random_device rd;
mt19937 mt(rd());
uniform_int_distribution<int> dice(1, 6);
uniform_real_distribution<double> score(0.0, 10.0);

using R = long double;

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);

  for (int n; cin >> n, n;) {
    vector<R> p(n);
    vector<vi> a(n);
    vector<vi> adj(n, vi(n));
    rep(i, n) {
      cin >> p[i];
      int m;
      cin >> m;
      a[i] = vi(m);
      for (auto &e : a[i])
        cin >> e, e--, adj[i][e] = true;
    }

    vector<vi> cango(n, vi(n));
    rep(i, n) {
      cango[i][i] = true;
      for (auto &j : a[i]) {
        cango[i][j] = true;
      }
    }
    rep(k, n) rep(i, n) rep(j, n) cango[i][j] |= (cango[i][k] & cango[k][j]);

    int m = 0;
    vi group(n, -1);
    rep(i, n) {
      if (group[i] != -1)
        continue;
      rep(j, i, n) {
        if (cango[i][j] & cango[j][i]) {
          assert(group[j] == -1);
          group[j] = m;
        }
      }
      m++;
    }

    vector<set<int>> edge(m);
    rep(i, n) {
      rep(j, n) {
        if (group[i] == group[j])
          continue;
        if (adj[i][j]) {
          edge[group[j]].insert(group[i]);
        }
      }
    }

    vector<R> q(m, 1.0);
    rep(i, n) { q[group[i]] *= p[i]; }

    R res = 1.0;
    rep(i, m) {
      if (edge[i].size() >= 1)
        continue;
      res *= ((R)1.0 - q[i]);
    }

    cout.precision(10);
    cout << fixed << res << endl;
  }

  return 0;
}

Error: WA

Fixed submission:

#include <bits/stdc++.h>

#define _overload(_1, _2, _3, name, ...) name
#define _rep(i, n) _range(i, 0, n)
#define _range(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rep(...) _overload(__VA_ARGS__, _range, _rep, )(__VA_ARGS__)

#define _rrep(i, n) _rrange(i, n, 0)
#define _rrange(i, a, b) for (int i = (int)(a)-1; i >= (int)(b); --i)
#define rrep(...) _overload(__VA_ARGS__, _rrange, _rrep, )(__VA_ARGS__)

#define _all(arg) begin(arg), end(arg)
#define uniq(arg) sort(_all(arg)), (arg).erase(unique(_all(arg)), end(arg))
#define getidx(ary, key) lower_bound(_all(ary), key) - begin(ary)
#define clr(a, b) memset((a), (b), sizeof(a))
#define bit(n) (1LL << (n))

// #define DEBUG

#ifdef DEBUG
#define dump(...) fprintf(stderr, __VA_ARGS__)
#else
#define dump(...)
#endif

template <class T> bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T> bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}

using namespace std;
using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;

const double EPS = 1e-10;
const double PI = acos(-1.0);
const ll inf = 1LL << 62;
const ll mod = 1000000007LL;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

ll extgcd(ll a, ll b, ll &x, ll &y) {
  x = 1, y = 0;
  ll g = a;
  if (b != 0)
    g = extgcd(b, a % b, y, x), y -= a / b * x;
  return g;
}
ll ADD(const ll &a, const ll &b, const ll &mod) { return (a + b) % mod; }
ll SUB(const ll &a, const ll &b, const ll &mod) { return (a - b + mod) % mod; }
ll MUL(const ll &a, const ll &b, const ll &mod) { return (1LL * a * b) % mod; }
ll DIV(const ll &a, const ll &b, const ll &mod) {
  ll x, y;
  extgcd(b, mod, x, y);
  return MUL(a, (x + mod) % mod, mod);
}

random_device rd;
mt19937 mt(rd());
uniform_int_distribution<int> dice(1, 6);
uniform_real_distribution<double> score(0.0, 10.0);

using R = long double;

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);

  for (int n; cin >> n, n;) {
    vector<R> p(n);
    vector<vi> a(n);
    vector<vi> adj(n, vi(n));
    rep(i, n) {
      cin >> p[i];
      p[i] = 1.0 - p[i];
      int m;
      cin >> m;
      a[i] = vi(m);
      for (auto &e : a[i])
        cin >> e, e--, adj[i][e] = true;
    }

    vector<vi> cango(n, vi(n));
    rep(i, n) {
      cango[i][i] = true;
      for (auto &j : a[i]) {
        cango[i][j] = true;
      }
    }
    rep(k, n) rep(i, n) rep(j, n) cango[i][j] |= (cango[i][k] & cango[k][j]);

    int m = 0;
    vi group(n, -1);
    rep(i, n) {
      if (group[i] != -1)
        continue;
      group[i] = m++;
      rep(j, i + 1, n) {
        if (cango[i][j] && cango[j][i]) {
          assert(group[j] == -1);
          group[j] = group[i];
        }
      }
    }

    vector<set<int>> edge(m);
    rep(i, n) {
      rep(j, n) {
        if (group[i] == group[j])
          continue;
        if (adj[i][j]) {
          edge[group[j]].insert(group[i]);
        }
      }
    }

    vector<R> q(m, 1.0);
    rep(i, n) { q[group[i]] *= (1.0 - p[i]); }
    for (auto &e : q)
      e = 1.0 - e;

    R res = 1.0;
    cerr << m << endl;
    rep(i, m) {
      if (edge[i].size() >= 1)
        continue;
      res *= q[i];
    }

    cout.precision(20);
    cout << res << endl;
  }

  return 0;
}