Problem p00372 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (int)n; i++)
#define all(c) (c).begin(), (c).end()
#define pb push_back
#define dbg(...)                                                               \\
  do {                                                                         \\
    cerr << __LINE__ << ": ";                                                  \\
    dbgprint(#__VA_ARGS__, __VA_ARGS__);                                       \\
  } while (0);

using namespace std;

namespace std {
template <class S, class T> struct hash<pair<S, T>> {
  size_t operator()(const pair<S, T> &p) const {
    return ((size_t)1e9 + 7) * hash<S>()(p.first) + hash<T>()(p.second);
  }
};
template <class T> struct hash<vector<T>> {
  size_t operator()(const vector<T> &v) const {
    size_t h = 0;
    for (auto i : v)
      h = h * ((size_t)1e9 + 7) + hash<T>()(i) + 1;
    return h;
  }
};
} // namespace std
template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "[ ";
  rep(i, v.size()) os << v[i] << (i == v.size() - 1 ? " ]" : ", ");
  return os;
}
template <class T> ostream &operator<<(ostream &os, const set<T> &v) {
  os << "{ ";
  for (const auto &i : v)
    os << i << ", ";
  return os << "}";
}
template <class T, class U>
ostream &operator<<(ostream &os, const map<T, U> &v) {
  os << "{";
  for (const auto &i : v)
    os << " " << i.first << ": " << i.second << ",";
  return os << "}";
}
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  return os << "(" << p.first << ", " << p.second << ")";
}
void dbgprint(const string &fmt) { cerr << endl; }
template <class H, class... T>
void dbgprint(const string &fmt, const H &h, const T &...r) {
  cerr << fmt.substr(0, fmt.find(",")) << "= " << h << " ";
  dbgprint(fmt.substr(fmt.find(",") + 1), r...);
}
typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pi;
const int inf = (int)1e9;
const double INF = 1e12, EPS = 1e-9;
void visit(const vector<vi> &g, int v, int u, vector<vector<int>> &tecomp,
           stack<int> &roots, stack<int> &S, vector<bool> &inS,
           vector<int> &num, int &time) {
  num[v] = ++time;
  S.push(v);
  inS[v] = true;
  roots.push(v);
  for (int w : g[v]) {
    if (num[w] == 0)
      visit(g, w, v, tecomp, roots, S, inS, num, time);
    else if (u != w && inS[w])
      while (roots.size() && num[roots.top()] > num[w])
        roots.pop();
  }
  if (v == roots.top()) {
    tecomp.push_back(vector<int>());
    while (S.size()) {
      int w = S.top();
      S.pop();
      inS[w] = false;
      tecomp.back().push_back(w);
      if (v == w)
        break;
    }
    roots.pop();
  }
}
vector<vi> calc_te(const vector<vi> &g) {
  const int n = g.size();
  vector<int> num(n);
  vector<bool> inS(n);
  vector<vi> tecomp;
  stack<int> roots, S;
  int time = 0;
  rep(u, n) if (num[u] == 0) {
    visit(g, u, n, tecomp, roots, S, inS, num, time);
  }
  return tecomp;
}
int main() {
  cin.tie(0);
  cin.sync_with_stdio(0);
  vector<vi> e, te;
  {
    int n, m;
    cin >> n >> m;
    vector<vi> g(n);
    rep(i, m) {
      int s, t;
      cin >> s >> t;
      g[s].pb(t);
      g[t].pb(s);
    }
    te = calc_te(g);
    vi to(n, -1);
    rep(i, te.size()) for (int j : te[i]) to[j] = i;

    e.resize(te.size());
    rep(i, n) for (int j : g[i]) if (to[i] != to[j]) e[to[i]].pb(to[j]);
  }
  // dbg(te); rep(i, te.size()) dbg(e[i]);

  vector<vi> sum(2, vi(e.size(), -1));
  function<void(int, int, int)> rec = [&](int c, int p, int u) {
    int &res = sum[u][c];
    if (res >= 0)
      return;
    res = 0;

    for (int i : e[c])
      if (i != p) {
        rep(j, 2) rec(i, c, j);
        if (u)
          res += sum[0][i];
        else
          res += max(sum[0][i], sum[1][i]);
      }
    if (u)
      res += te[c].size();
  };
  int ans = 0;
  rep(i, e.size()) if (sum[0][i] < 0) {
    rep(j, 2) rec(i, i, j);
    ans += max(sum[0][i], sum[1][i]);
  }
  cout << ans << endl;

  return 0;
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (int)n; i++)
#define all(c) (c).begin(), (c).end()
#define pb push_back
#define dbg(...)                                                               \\
  do {                                                                         \\
    cerr << __LINE__ << ": ";                                                  \\
    dbgprint(#__VA_ARGS__, __VA_ARGS__);                                       \\
  } while (0);

using namespace std;

namespace std {
template <class S, class T> struct hash<pair<S, T>> {
  size_t operator()(const pair<S, T> &p) const {
    return ((size_t)1e9 + 7) * hash<S>()(p.first) + hash<T>()(p.second);
  }
};
template <class T> struct hash<vector<T>> {
  size_t operator()(const vector<T> &v) const {
    size_t h = 0;
    for (auto i : v)
      h = h * ((size_t)1e9 + 7) + hash<T>()(i) + 1;
    return h;
  }
};
} // namespace std
template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "[ ";
  rep(i, v.size()) os << v[i] << (i == v.size() - 1 ? " ]" : ", ");
  return os;
}
template <class T> ostream &operator<<(ostream &os, const set<T> &v) {
  os << "{ ";
  for (const auto &i : v)
    os << i << ", ";
  return os << "}";
}
template <class T, class U>
ostream &operator<<(ostream &os, const map<T, U> &v) {
  os << "{";
  for (const auto &i : v)
    os << " " << i.first << ": " << i.second << ",";
  return os << "}";
}
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  return os << "(" << p.first << ", " << p.second << ")";
}
void dbgprint(const string &fmt) { cerr << endl; }
template <class H, class... T>
void dbgprint(const string &fmt, const H &h, const T &...r) {
  cerr << fmt.substr(0, fmt.find(",")) << "= " << h << " ";
  dbgprint(fmt.substr(fmt.find(",") + 1), r...);
}
typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pi;
const int inf = (int)1e9;
const double INF = 1e12, EPS = 1e-9;
void visit(const vector<vi> &g, int v, int u, vector<vector<int>> &tecomp,
           stack<int> &roots, stack<int> &S, vector<bool> &inS,
           vector<int> &num, int &time) {
  num[v] = ++time;
  S.push(v);
  inS[v] = true;
  roots.push(v);
  for (int w : g[v]) {
    if (num[w] == 0)
      visit(g, w, v, tecomp, roots, S, inS, num, time);
    else if (u != w && inS[w])
      while (num[roots.top()] > num[w])
        roots.pop();
  }
  if (v == roots.top()) {
    tecomp.push_back(vector<int>());
    while (1) {
      int w = S.top();
      S.pop();
      inS[w] = false;
      tecomp.back().push_back(w);
      if (v == w)
        break;
    }
    roots.pop();
  }
}
vector<vi> calc_te(const vector<vi> &g) {
  const int n = g.size();
  vector<int> num(n);
  vector<bool> inS(n);
  vector<vi> tecomp;
  stack<int> roots, S;
  int time = 0;
  rep(u, n) if (num[u] == 0) {
    visit(g, u, n, tecomp, roots, S, inS, num, time);
  }
  return tecomp;
}
int main() {
  cin.tie(0);
  cin.sync_with_stdio(0);
  vector<vi> e, te;
  {
    int n, m;
    cin >> n >> m;
    vector<vi> g(n);
    rep(i, m) {
      int s, t;
      cin >> s >> t;
      g[s].pb(t);
      g[t].pb(s);
    }
    te = calc_te(g);
    vi to(n, -1);
    rep(i, te.size()) for (int j : te[i]) to[j] = i;

    e.resize(te.size());
    rep(i, n) for (int j : g[i]) if (to[i] != to[j]) e[to[i]].pb(to[j]);
  }
  // dbg(te); rep(i, te.size()) dbg(e[i]);

  vector<vi> sum(2, vi(e.size(), -1));
  function<void(int, int, int)> rec = [&](int c, int p, int u) {
    for (int i : e[c])
      if (i != p)
        rep(j, 2) rec(i, c, j);
    int &res = sum[u][c];
    if (res >= 0)
      return;
    res = 0;

    for (int i : e[c])
      if (i != p) {
        if (u)
          res += sum[0][i];
        else
          res += max(sum[0][i], sum[1][i]);
      }
    if (u)
      res += te[c].size();
  };
  int ans = 0;
  rep(i, e.size()) if (sum[0][i] < 0) {
    rep(j, 2) rec(i, i, j);
    ans += max(sum[0][i], sum[1][i]);
  }
  cout << ans << endl;

  return 0;
}