Problem p03690 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define SZ(x) ((int)(x).size())
using namespace std;

void noSol() {
  cout << "-1\n";
  exit(0);
}

template <class T> vector<T> sorted(const vector<T> &a) {
  vector<T> b = a;
  sort(b.begin(), b.end());
  return b;
}

vector<int> cc;
vector<vector<int>> graph;

int dfs(int node, int ccc) {
  cc[node] = ccc;
  int ret = SZ(graph[node]);
  for (int to : graph[node]) {
    if (cc[to] == -1) {
      ret += dfs(to, ccc);
    }
  }
  return ret;
}

int solve(vector<int> a, vector<int> b) {
  vector<int> all = a;
  all.insert(all.end(), b.begin(), b.end());
  sort(all.begin(), all.end());
  all.erase(unique(all.begin(), all.end()), all.end());
  for (int &x : a) {
    x = lower_bound(all.begin(), all.end(), x) - all.begin();
  }
  for (int &x : b) {
    x = lower_bound(all.begin(), all.end(), x) - all.begin();
  }
  int n = SZ(a);
  cc = vector<int>(n, -1);
  graph = vector<vector<int>>(n);
  for (int i = 0; i < n; ++i) {
    if (a[i] != b[i]) {
      graph[a[i]].push_back(b[i]);
      graph[b[i]].push_back(a[i]);
    }
  }
  int ccc = 0;
  int ans = 0;
  for (int i = 0; i < n; ++i) {
    if (cc[i] == -1 && !graph[i].empty()) {
      ans += dfs(i, ccc++);
    }
  }
  ans /= 2;
  ans += ccc;
  return ans;
}

int main() {
#ifdef LOCAL_RUN
  freopen("task.in", "r", stdin);
  freopen("task.out", "w", stdout);
// freopen("task.err", "w", stderr);
#endif // ONLINE_JUDGE
  ios::sync_with_stdio(false);
  cin.tie(0);

  int n;
  cin >> n;
  vector<int> a(n), b(n);
  for (int i = 0; i < n; ++i) {
    cin >> a[i];
  }
  for (int i = 0; i < n; ++i) {
    cin >> b[i];
  }
  const int INF = 0x3f3f3f3f;
  int ans = INF;
  if (sorted(a) == sorted(b)) {
    ans = solve(a, b);
    int x = 0;
    for (int val : a)
      x ^= val;
    for (int i = 0; i < n; ++i) {
      if (a[i] != b[i] && a[i] == x) {
        ans--;
        break;
      }
    }
    cout << ans << '\n';
  } else {
    throw;
    map<int, int> ma, mb;
    int x = 0;
    for (int val : a)
      x ^= val;
    for (int val : a)
      ma[val]++;
    for (int val : b)
      mb[val]++;
    int add = 0;
    for (const pair<int, int> &p : ma) {
      add += max(0, p.second - mb[p.first]);
    }
    if (add > 1) {
      noSol();
    }
    int bad = -1;
    for (const pair<int, int> &p : ma) {
      if (p.second > mb[p.first]) {
        bad = p.first;
        break;
      }
    }
    if (bad == x) {
      noSol();
    }
    int pos = -1;
    for (int i = 0; i < n; ++i) {
      if (a[i] == bad && a[i] != b[i] && b[i] != x) {
        pos = i;
        swap(x, a[i]);
        break;
      }
    }
    if (pos != -1) {
      int ans = solve(a, b) - 1;
      // for (int i = 0; i < n; ++i) {
      //     if (a[i] != b[i] && a[i] == x && cc[i] != cc[pos]) {
      //         ans--;
      //         break;
      //     }
      // }
      cout << ans << '\n';
    } else {
      for (int i = 0; i < n; ++i) {
        if (a[i] == bad && a[i] != b[i]) {
          pos = i;
          swap(x, a[i]);
          break;
        }
      }
      int ans = solve(a, b) + 1;
      for (int i = 0; i < n; ++i) {
        if (a[i] == a[pos] && a[i] != b[i]) {
          ans--;
          break;
        }
      }
      // for (int i = 0; i < n; ++i) {
      //     if (a[i] != b[i] && a[i] == x && cc[i] != cc[pos]) {
      //         ans--;
      //         break;
      //     }
      // }
      cout << ans << '\n';
    }
  }
}


Fixed submission:
#include <bits/stdc++.h>
#define SZ(x) ((int)(x).size())
using namespace std;

void noSol() {
  cout << "-1\n";
  exit(0);
}

template <class T> vector<T> sorted(const vector<T> &a) {
  vector<T> b = a;
  sort(b.begin(), b.end());
  return b;
}

vector<int> cc;
vector<vector<int>> graph;

int dfs(int node, int ccc) {
  cc[node] = ccc;
  int ret = SZ(graph[node]);
  for (int to : graph[node]) {
    if (cc[to] == -1) {
      ret += dfs(to, ccc);
    }
  }
  return ret;
}

int solve(vector<int> a, vector<int> b) {
  vector<int> all = a;
  all.insert(all.end(), b.begin(), b.end());
  sort(all.begin(), all.end());
  all.erase(unique(all.begin(), all.end()), all.end());
  for (int &x : a) {
    x = lower_bound(all.begin(), all.end(), x) - all.begin();
  }
  for (int &x : b) {
    x = lower_bound(all.begin(), all.end(), x) - all.begin();
  }
  int n = SZ(a);
  cc = vector<int>(n, -1);
  graph = vector<vector<int>>(n);
  for (int i = 0; i < n; ++i) {
    if (a[i] != b[i]) {
      graph[a[i]].push_back(b[i]);
      graph[b[i]].push_back(a[i]);
    }
  }
  int ccc = 0;
  int ans = 0;
  for (int i = 0; i < n; ++i) {
    if (cc[i] == -1 && !graph[i].empty()) {
      ans += dfs(i, ccc++);
    }
  }
  ans /= 2;
  ans += ccc;
  return ans;
}

int main() {
#ifdef LOCAL_RUN
  freopen("task.in", "r", stdin);
  freopen("task.out", "w", stdout);
// freopen("task.err", "w", stderr);
#endif // ONLINE_JUDGE
  ios::sync_with_stdio(false);
  cin.tie(0);

  int n;
  cin >> n;
  vector<int> a(n), b(n);
  for (int i = 0; i < n; ++i) {
    cin >> a[i];
  }
  for (int i = 0; i < n; ++i) {
    cin >> b[i];
  }
  const int INF = 0x3f3f3f3f;
  int ans = INF;
  if (sorted(a) == sorted(b)) {
    ans = solve(a, b);
    int x = 0;
    for (int val : a)
      x ^= val;
    for (int i = 0; i < n; ++i) {
      if (a[i] != b[i] && a[i] == x) {
        ans--;
        break;
      }
    }
    cout << ans << '\n';
  } else {
    map<int, int> ma, mb;
    int x = 0;
    for (int val : a)
      x ^= val;
    for (int val : a)
      ma[val]++;
    for (int val : b)
      mb[val]++;
    int add = 0;
    for (const pair<int, int> &p : ma) {
      add += max(0, p.second - mb[p.first]);
    }
    if (add > 1) {
      noSol();
    }
    int bad = -1;
    for (const pair<int, int> &p : ma) {
      if (p.second > mb[p.first]) {
        bad = p.first;
        break;
      }
    }
    if (bad == x) {
      noSol();
    }
    int pos = -1;
    for (int i = 0; i < n; ++i) {
      if (a[i] == bad && a[i] != b[i] && b[i] != x) {
        pos = i;
        swap(x, a[i]);
        break;
      }
    }
    if (pos != -1) {
      int ans = solve(a, b) - 1;
      // for (int i = 0; i < n; ++i) {
      //     if (a[i] != b[i] && a[i] == x && cc[i] != cc[pos]) {
      //         ans--;
      //         break;
      //     }
      // }
      cout << ans << '\n';
    } else {
      for (int i = 0; i < n; ++i) {
        if (a[i] == bad && a[i] != b[i]) {
          pos = i;
          swap(x, a[i]);
          break;
        }
      }
      int ans = solve(a, b) + 1;
      for (int i = 0; i < n; ++i) {
        if (a[i] == a[pos] && a[i] != b[i]) {
          ans--;
          break;
        }
      }
      // for (int i = 0; i < n; ++i) {
      //     if (a[i] != b[i] && a[i] == x && cc[i] != cc[pos]) {
      //         ans--;
      //         break;
      //     }
      // }
      cout << ans << '\n';
    }
  }
}