Problem p02581 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
using namespace std;

#define int long long
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define reps(i, n) for (int i = 1; i <= (int)(n); i++)
#define all(x) (x).begin(), (x).end()
#define uniq(x) (x).erase(unique(all(x)), (x).end())
#define bit(n) (1LL << (n))
#define dump(x) cerr << #x " = " << (x) << endl
using vint = vector<int>;
using vvint = vector<vint>;
using pint = pair<int, int>;
using vpint = vector<pint>;
template <typename T>
using priority_queue_rev = priority_queue<T, vector<T>, greater<T>>;
constexpr double PI = 3.1415926535897932384626433832795028;
constexpr int DY[9] = {0, 1, 0, -1, 1, 1, -1, -1, 0};
constexpr int DX[9] = {1, 0, -1, 0, 1, -1, -1, 1, 0};
int sign(int x) { return (x > 0) - (x < 0); }
int gcd(int a, int b) {
  while (b) {
    swap(a %= b, b);
  }
  return a;
}
int lcm(int a, int b) { return a / gcd(a, b) * b; }
int cdiv(int a, int b) { return (a - 1 + b) / b; }
template <typename T> void fin(T mes) {
  cout << mes << endl;
  exit(0);
}
template <typename T, typename U> bool chmax(T &a, const U &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T, typename U> bool chmin(T &a, const U &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &rhs) {
  os << "(" << rhs.first << ", " << rhs.second << ")";
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &rhs) {
  os << "{";
  for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
    os << *itr << (next(itr) != rhs.end() ? ", " : "");
  }
  os << "}";
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const deque<T> &rhs) {
  os << "{";
  for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
    os << *itr << (next(itr) != rhs.end() ? ", " : "");
  }
  os << "}";
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const set<T> &rhs) {
  os << "{";
  for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
    os << *itr << (next(itr) != rhs.end() ? ", " : "");
  }
  os << "}";
  return os;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, const map<T, U> &rhs) {
  os << "{";
  for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
    os << *itr << (next(itr) != rhs.end() ? ", " : "");
  }
  os << "}";
  return os;
}
struct setup {
  static constexpr int PREC = 20;
  setup() {
    cout << fixed << setprecision(PREC);
    cerr << fixed << setprecision(PREC);
  };
} setup;

signed main() {
  int N;
  cin >> N;
  vint A(3 * N);
  rep(i, 3 * N) { cin >> A[i], A[i]--; }
  int bias = 0, ans = 0;
  vvint dp(N, vint(N, -1));
  vint rmax(N, -1);
  dp[A[0]][A[1]] = dp[A[1]][A[0]] = 0;
  rmax[A[0]] = rmax[A[1]] = 0;
  rep(i, N - 1) {
    vint a = {A[3 * i + 2], A[3 * i + 3], A[3 * i + 4]};
    if (a[0] == a[1] && a[1] == a[2]) {
      bias++;
      continue;
    }
    vector<tuple<int, int, int>> query;
    rep(j, 3) {
      vint aa;
      rep(k, 3) {
        if (j != k) {
          aa.emplace_back(a[k]);
        }
      }
      query.emplace_back(aa[0], aa[1], ans);
      if (dp[a[j]][a[j]] >= 0) {
        query.emplace_back(aa[0], aa[1], dp[a[j]][a[j]] + 1);
      }
      rep(k, N) {
        query.emplace_back(k, a[j], rmax[k]);
        if (aa[0] == aa[1] && dp[k][aa[0]] >= 0) {
          query.emplace_back(k, a[j], dp[k][aa[0]] + 1);
        }
      }
    }
    rep(j, query.size()) {
      auto [x, y, v] = query[j];
      chmax(dp[x][y], v), chmax(dp[y][x], v);
      chmax(rmax[x], v), chmax(rmax[y], v);
      chmax(ans, v);
    }
  }
  chmax(ans, dp[A[3 * N - 1]][A[3 * N - 1]] + 1);
  ans += bias;
  cout << ans << endl;
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
using namespace std;

#define int long long
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define reps(i, n) for (int i = 1; i <= (int)(n); i++)
#define all(x) (x).begin(), (x).end()
#define uniq(x) (x).erase(unique(all(x)), (x).end())
#define bit(n) (1LL << (n))
#define dump(x) cerr << #x " = " << (x) << endl
using vint = vector<int>;
using vvint = vector<vint>;
using pint = pair<int, int>;
using vpint = vector<pint>;
template <typename T>
using priority_queue_rev = priority_queue<T, vector<T>, greater<T>>;
constexpr double PI = 3.1415926535897932384626433832795028;
constexpr int DY[9] = {0, 1, 0, -1, 1, 1, -1, -1, 0};
constexpr int DX[9] = {1, 0, -1, 0, 1, -1, -1, 1, 0};
int sign(int x) { return (x > 0) - (x < 0); }
int gcd(int a, int b) {
  while (b) {
    swap(a %= b, b);
  }
  return a;
}
int lcm(int a, int b) { return a / gcd(a, b) * b; }
int cdiv(int a, int b) { return (a - 1 + b) / b; }
template <typename T> void fin(T mes) {
  cout << mes << endl;
  exit(0);
}
template <typename T, typename U> bool chmax(T &a, const U &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T, typename U> bool chmin(T &a, const U &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &rhs) {
  os << "(" << rhs.first << ", " << rhs.second << ")";
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &rhs) {
  os << "{";
  for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
    os << *itr << (next(itr) != rhs.end() ? ", " : "");
  }
  os << "}";
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const deque<T> &rhs) {
  os << "{";
  for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
    os << *itr << (next(itr) != rhs.end() ? ", " : "");
  }
  os << "}";
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const set<T> &rhs) {
  os << "{";
  for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
    os << *itr << (next(itr) != rhs.end() ? ", " : "");
  }
  os << "}";
  return os;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, const map<T, U> &rhs) {
  os << "{";
  for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
    os << *itr << (next(itr) != rhs.end() ? ", " : "");
  }
  os << "}";
  return os;
}
struct setup {
  static constexpr int PREC = 20;
  setup() {
    cout << fixed << setprecision(PREC);
    cerr << fixed << setprecision(PREC);
  };
} setup;

signed main() {
  int N;
  cin >> N;
  vint A(3 * N);
  rep(i, 3 * N) { cin >> A[i], A[i]--; }
  int bias = 0, ans = 0;
  vvint dp(N, vint(N, -1));
  vint rmax(N, -1);
  dp[A[0]][A[1]] = dp[A[1]][A[0]] = 0;
  rmax[A[0]] = rmax[A[1]] = 0;
  rep(i, N - 1) {
    vint a = {A[3 * i + 2], A[3 * i + 3], A[3 * i + 4]};
    if (a[0] == a[1] && a[1] == a[2]) {
      bias++;
      continue;
    }
    vector<tuple<int, int, int>> query;
    rep(j, 3) {
      vint aa;
      rep(k, 3) {
        if (j != k) {
          aa.emplace_back(a[k]);
        }
      }
      query.emplace_back(aa[0], aa[1], ans);
      if (dp[a[j]][a[j]] >= 0) {
        query.emplace_back(aa[0], aa[1], dp[a[j]][a[j]] + 1);
      }
      rep(k, N) {
        query.emplace_back(k, a[j], rmax[k]);
        if (aa[0] == aa[1] && dp[k][aa[0]] >= 0) {
          query.emplace_back(k, a[j], dp[k][aa[0]] + 1);
        }
      }
    }
    rep(j, query.size()) {
      auto [x, y, v] = query[j];
      chmax(dp[x][y], v), chmax(dp[y][x], v);
      chmax(rmax[x], v), chmax(rmax[y], v);
      chmax(ans, v);
    }
    rep(i, N) {
      rep(j, N) { cerr << dp[i][j] << " "; }
      cerr << endl;
    }
    cerr << endl;
  }
  dump(ans);
  chmax(ans, dp[A[3 * N - 1]][A[3 * N - 1]] + 1);
  ans += bias;
  cout << ans << endl;
}