Problem p01187 (C++) — buggy submission, verdict: Runtime Error

#include "bits/stdc++.h"
using namespace std;
#ifdef _DEBUG
#include "dump.hpp"
#else
#define dump(...)
#endif

// #define int long long
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define all(c) begin(c), end(c)
const int INF =
    sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)(1e9) + 7;
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}

struct Dinic {
  using Flow = int;
  struct Edge {
    int to, rev;
    Flow cap;
    Edge() {}
    Edge(int to, int rev, Flow cap) : to(to), rev(rev), cap(cap) {}
  };
  int n;
  vector<vector<Edge>> g;
  vector<bool> used;
  vector<int> level;
  vector<int> iter;
  Dinic(int n) : n(n), g(n), used(n), level(n), iter(n){};
  void addArc(int from, int to, Flow cap) {
    g[from].emplace_back(to, (int)g[to].size(), cap);
    g[to].emplace_back(from, (int)g[from].size() - 1, 0);
  }
  void addEdge(int a, int b, Flow cap) {
    g[a].emplace_back(b, (int)g[b].size(), cap);
    g[b].emplace_back(a, (int)g[a].size() - 1, cap);
  }
  Flow maximumFlow(int s, int t) {
    Flow total = 0;
    while (true) {
      levelize(s);
      if (level[t] < 0)
        return total;
      fill(iter.begin(), iter.end(), 0);
      Flow f;
      while (true) {
        f = augment(s, t, INF);
        if (f == 0)
          break;
        total += f;
      }
    }
  }
  Flow augment(int v, int t, Flow f) {
    if (v == t)
      return f;
    for (int &i = iter[v]; i < g[v].size(); i++) {
      Edge &e = g[v][i];
      if (e.cap > 0 && level[v] < level[e.to]) {
        Flow d = augment(e.to, t, min(f, e.cap));
        if (d > 0) {
          e.cap -= d;
          g[e.to][e.rev].cap += d;
          return d;
        }
      }
    }
    return 0;
  }
  void levelize(int s) {
    fill(level.begin(), level.end(), -1);
    queue<int> q;
    level[s] = 0;
    q.push(s);
    while (q.size()) {
      int v = q.front();
      q.pop();
      for (int i = 0; i < g[v].size(); i++) {
        Edge &e = g[v][i];
        if (e.cap > 0 && level[e.to] < 0) {
          level[e.to] = level[v] + 1;
          q.push(e.to);
        }
      }
    }
  }
};

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  for (int N; cin >> N && N;) {
    int M;
    cin >> M;
    Dinic dinic(M + N + 2);
    int s = dinic.n - 2, t = s + 1;
    unordered_map<int, int> mp;
    rep(i, 0, M) {
      int d;
      cin >> d;
      mp[d] = i;
    }
    rep(i, 0, N) {
      int m;
      cin >> m;
      rep(j, 0, m) {
        int d;
        cin >> d;
        if (mp.count(d))
          dinic.addArc(mp[d], M + i, 1);
      }
    }
    rep(i, 0, M) dinic.addArc(s, i, 1);
    rep(i, 0, N) dinic.addArc(M + i, t, 1);
    cout << dinic.maximumFlow(s, t) << endl;
  }
  return 0;
}

Error: 0

Fixed submission:

#include "bits/stdc++.h"
using namespace std;
#ifdef _DEBUG
#include "dump.hpp"
#else
#define dump(...)
#endif

// #define int long long
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define all(c) begin(c), end(c)
const int INF =
    sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)(1e9) + 7;
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}

struct Dinic {
  using Flow = int;
  struct Edge {
    int to, rev;
    Flow cap;
    Edge() {}
    Edge(int to, int rev, Flow cap) : to(to), rev(rev), cap(cap) {}
  };
  int n;
  vector<vector<Edge>> g;
  vector<bool> used;
  vector<int> level;
  vector<int> iter;
  Dinic(int n) : n(n), g(n), used(n), level(n), iter(n){};
  void addArc(int from, int to, Flow cap) {
    g[from].emplace_back(to, (int)g[to].size(), cap);
    g[to].emplace_back(from, (int)g[from].size() - 1, 0);
  }
  void addEdge(int a, int b, Flow cap) {
    g[a].emplace_back(b, (int)g[b].size(), cap);
    g[b].emplace_back(a, (int)g[a].size() - 1, cap);
  }
  Flow maximumFlow(int s, int t) {
    Flow total = 0;
    while (true) {
      levelize(s);
      if (level[t] < 0)
        return total;
      fill(iter.begin(), iter.end(), 0);
      Flow f;
      while (true) {
        f = augment(s, t, INF);
        if (f == 0)
          break;
        total += f;
      }
    }
  }
  Flow augment(int v, int t, Flow f) {
    if (v == t)
      return f;
    for (int &i = iter[v]; i < g[v].size(); i++) {
      Edge &e = g[v][i];
      if (e.cap > 0 && level[v] < level[e.to]) {
        Flow d = augment(e.to, t, min(f, e.cap));
        if (d > 0) {
          e.cap -= d;
          g[e.to][e.rev].cap += d;
          return d;
        }
      }
    }
    return 0;
  }
  void levelize(int s) {
    fill(level.begin(), level.end(), -1);
    queue<int> q;
    level[s] = 0;
    q.push(s);
    while (q.size()) {
      int v = q.front();
      q.pop();
      for (int i = 0; i < g[v].size(); i++) {
        Edge &e = g[v][i];
        if (e.cap > 0 && level[e.to] < 0) {
          level[e.to] = level[v] + 1;
          q.push(e.to);
        }
      }
    }
  }
};

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  for (int N; cin >> N && N;) {
    int M;
    cin >> M;
    Dinic dinic(M + N + 2);
    int s = dinic.n - 2, t = s + 1;
    unordered_map<int, int> mp;
    rep(i, 0, M) {
      int d;
      cin >> d;
      mp[d] = i;
    }
    rep(i, 0, N) {
      int M;
      cin >> M;
      rep(j, 0, M) {
        int d;
        cin >> d;
        if (mp.count(d))
          dinic.addArc(mp[d], M + i, 1);
      }
    }
    rep(i, 0, M) dinic.addArc(s, i, 1);
    rep(i, 0, N) dinic.addArc(M + i, t, 1);
    cout << dinic.maximumFlow(s, t) << endl;
  }
  return 0;
}