Problem p02716 (C++) — buggy submission, verdict: Time Limit Exceeded

/*
 * じょえチャンネル
 * 高評価・チャンネル登録よろしくおねがいします！
 * https://www.youtube.com/channel/UCRXsI3FL_kvaVL9zoolBfbQ
 */

#include <bits/stdc++.h>

// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")

#define f(i, n) for (int i = 0; i < (n); i++)

#define inf (int)(3e18)

// here!!!
//  define int long long !!!!!

#define int long long

// define int long long !!!!!

#define mod (int)((1e9) + 7)

#define intt long long
#define itn long long
#define P pair<int, int>

#define rep(i, n) for (int i = 0; i < n; i++)
#define REP(i, n) for (int i = 1; i <= n; i++)

#define ALL(v) v.begin(), v.end()

using namespace std;

// Library
// モッドパウ
inline int modpow(int x, int y, int m = mod) {
  int res = 1;
  while (y) {
    if (y % 2) {
      res *= x;
      res %= m;
    }
    x = x * x % m;
    y /= 2;
  }
  return res;
}

int mypow(int x, int y) {
  int res = 1;
  while (y) {
    if (y % 2) {
      res *= x;
    }
    x = x * x;
    y /= 2;
  }
  return res;
}
// is the number (x) a prime number?
bool prime(int x) {
  for (int i = 2; i * i <= x; i++) {
    if (!(x % i)) {
      return false;
    }
  }
  return true;
}

// saidai-kouyakusuu
inline int gcd(int x, int y) {
  if (!y) {
    return x;
  }
  return gcd(y, x % y);
}

// number of keta
int keta(int x) {
  int ans = 0;
  while (x) {
    x /= 10;
    ans++;
  }
  return ans;
}

// sum of keta
int ketasum(int x) {
  int ans = 0;
  while (x) {
    ans += x % 10;
    x /= 10;
  }
  return ans;
}

inline int lcm(int x, int y) {
  int ans = x / gcd(x, y) * y;
  return ans;
}
int twobeki(int x) {
  int ans = 0;
  while (1) {
    if (!(x & 1)) {
      ans++;
      x /= 2;
    } else {
      break;
    }
  }
  return ans;
}

template <class T, class U> inline bool chmax(T &lhs, const U &rhs) {
  if (lhs < rhs) {
    lhs = rhs;
    return 1;
  }
  return 0;
}
template <class T, class U> inline bool chmin(T &lhs, const U &rhs) {
  if (lhs > rhs) {
    lhs = rhs;
    return 1;
  }
  return 0;
}
void Yes() { cout << "Yes" << endl; }
void No() { cout << "No" << endl; }
void YES() { cout << "YES" << endl; }
void NO() { cout << "NO" << endl; }

int kai(int x, int y) {
  int res = 1;
  for (int i = x - y + 1; i <= x; i++) {
    res *= i;
    res %= mod;
  }
  return res;
}

int comb(int x, int y) {
  if (y > x)
    return 0;
  return kai(x, y) * modpow(kai(y, y), mod - 2) % mod;
}

#define fin(i) scanf("%lld", &i)
#define fout(i) printf("%lld", i)
#define fendl printf("\\n")
// Library-End

class modInt {
  int value, modulo;

public:
  modInt() : value(0), modulo(mod) { value = 0; }
  template <typename T>
  modInt(T value = 0, int modulo = mod) : value(value), modulo(modulo) {
    if (value < 0) {
      value = -value;
      value %= modulo;
      value = -value;
      value += modulo;
    }
    this->value = value % modulo;
  }
  inline operator int() const { return value; }
  inline modInt &operator+=(modInt x) {
    value += x.value;
    if (value >= modulo)
      value -= modulo;
    return *this;
  }
  inline modInt &operator++() {
    if (value == modulo - 1)
      value = 0;
    else
      value++;
    return *this;
  }
  inline modInt &operator-() const { return modInt(0) -= *this; }
  inline modInt &operator-=(modInt x) {
    value -= x.value;
    if (value < 0)
      value += modulo;
    return *this;
  }
  inline modInt &operator--() {
    if (value == 0)
      value = modulo - 1;
    else
      value--;
    return *this;
  }
  inline modInt &operator*=(modInt x) {
    value = value * x.value % modulo;
    return *this;
  }
  inline modInt &operator/=(modInt x) { return operator*=(x.inv()); }
  inline modInt inv() { return modpow(*this, modulo - 2); }
  template <typename T> modInt operator+(T x) { return modInt(*this) += x; }
  template <typename T> modInt &operator+=(T x) {
    return operator+=(modInt(x, modulo));
  }
  template <typename T> modInt operator-(T x) { return modInt(*this) -= x; }
  template <typename T> modInt &operator-=(T x) {
    return operator-=(modInt(x, modulo));
  }
  template <typename T> modInt operator*(T x) { return modInt(*this) *= x; }
  template <typename T> modInt &operator*=(T x) {
    return operator*=(modInt(x, modulo));
  }
  template <typename T> modInt operator/(T x) { return modInt(*this) /= x; }
  template <typename T> modInt &operator/=(T x) {
    return operator/=(modInt(x, modulo));
  }
};
istream &operator>>(istream &ist, modInt &x) {
  int a;
  ist >> a;
  x = a;
  return ist;
}
#define vecin(v)                                                               \\
  for (int i = 0; i < v.size(); i++)                                           \\
    scanf("%lld", &v[i]);
#define vecout(v)                                                              \\
  {                                                                            \\
    for (int i = 0; i < v.size(); i++)                                         \\
      printf("%lld\\n", v[i]);                                                  \\
  }
#define endl "\\n" // interactive の時に注意！！！
// SegTree
template <class T> class SegTree {
  int n;                       // 葉の数
  vector<T> data;              // データを格納するvector
  T def;                       // 初期値かつ単位元
  function<T(T, T)> operation; // 区間クエリで使う処理
  function<T(T, T)> update;    // 点更新で使う処理

  // 区間[a,b)の総和。ノードk=[l,r)に着目している。
  T _query(int a, int b, int k, int l, int r) {
    if (r <= a || b <= l)
      return def; // 交差しない
    if (a <= l && r <= b)
      return data[k]; // a,l,r,bの順で完全に含まれる
    else {
      T c1 = _query(a, b, 2 * k + 1, l, (l + r) / 2); // 左の子
      T c2 = _query(a, b, 2 * k + 2, (l + r) / 2, r); // 右の子
      return operation(c1, c2);
    }
  }

public:
  // _n:必要サイズ, _def:初期値かつ単位元, _operation:クエリ関数,
  // _update:更新関数
  SegTree(size_t _n, T _def, function<T(T, T)> _operation,
          function<T(T, T)> _update)
      : def(_def), operation(_operation), update(_update) {
    n = 1;
    while (n < _n) {
      n *= 2;
    }
    data = vector<T>(2 * n - 1, def);
  }

  // 場所i(0-indexed)の値をxで更新
  void change(int i, T x) {
    i += n - 1;
    data[i] = update(data[i], x);
    while (i > 0) {
      i = (i - 1) / 2;
      data[i] = operation(data[i * 2 + 1], data[i * 2 + 2]);
    }
  }

  // [a, b)の区間クエリを実行
  T query(int a, int b) { return _query(a, b, 0, 0, n); }

  // 添字でアクセス
  T operator[](int i) { return data[i + n - 1]; }
};

#define R_MIN ([](long long a, long long b) { return min(a, b); })
#define R_MAX ([](long long a, long long b) { return max(a, b); })
#define R_SUM ([](long long a, long long b) { return a + b; })

#define NORMAL_UPDATE ([](long long a, long long b) { return b; })
#define ADD_UPDATE ([](long long a, long long b) { return a + b; })
#define MINUS_UPDATE ([](long long a, long long b) { return a - b; }

class Union_Find {
  vector<int> par;
  vector<int> rankmy;
  vector<int> ookisa;

public:
  Union_Find(int size) {
    par = vector<int>(size);
    rankmy = vector<int>(size);
    ookisa = vector<int>(size);
    for (int i = 0; i < size; i++) {
      par[i] = i;
      ookisa[i] = 1;
    }
  }

  int find(int x) {
    if (par[x] == x) {
      return x;
    }
    return par[x] = find(par[x]);
  }

  void unite(int x, int y) {
    x = find(x);
    y = find(y);
    if (x == y) {
      return;
    }
    if (rankmy[x] < rankmy[y]) {
      par[x] = y;
      ookisa[y] += ookisa[x];
      ookisa[x] = 0;
    } else {
      par[y] = x;
      ookisa[x] += ookisa[y];
      ookisa[y] = 0;
      if (rankmy[x] == rankmy[y]) {
        rankmy[x]++;
      }
    }
  }
  int size(int i) {
    i = find(i);
    return ookisa[i];
  }
  bool same(int x, int y) { return find(x) == find(y); }
};

// Union-Find-End

int n, k, a[200004], ans, hiku, now, sm;
int dp[200004][3];

signed main() {
  ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  cin >> n;
  REP(i, n) cin >> a[i];
  ans = 0 - inf;
  if (n & 1) {
    int k = 1 + (n - 3) / 2;
    REP(i, k) {
      dp[i][0] = dp[i - 1][0] + a[i * 2 - 1];
      dp[i][1] = dp[i - 1][1] + a[i * 2];
      chmax(dp[i][1], dp[i][0]);
      dp[i][2] = dp[i - 1][2] + a[i * 2 + 1];
      chmax(dp[i][2], dp[i][1]);
    }
    chmax(ans, dp[k][2]);
  } else {
    REP(i, n / 2) {
      dp[i][0] = dp[i - 1][0] + a[i * 2 - 1];
      dp[i][1] = dp[i - 1][1] + a[i * 2];
      chmax(dp[i][1], dp[i][0]);
    }
    chmax(ans, dp[n / 2][1]);
  }
  cout << ans << endl;
}


Error: TLE

Fixed submission:

/*
 * じょえチャンネル
 * 高評価・チャンネル登録よろしくおねがいします！
 * https://www.youtube.com/channel/UCRXsI3FL_kvaVL9zoolBfbQ
 */

#include <bits/stdc++.h>

#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")

#define f(i, n) for (int i = 0; i < (n); i++)

#define inf (int)(3e18)

// here!!!
//  define int long long !!!!!

#define int long long

// define int long long !!!!!

#define mod (int)((1e9) + 7)

#define intt long long
#define itn long long
#define P pair<int, int>

#define rep(i, n) for (int i = 0; i < n; i++)
#define REP(i, n) for (int i = 1; i <= n; i++)

#define ALL(v) v.begin(), v.end()

using namespace std;

// Library
// モッドパウ
inline int modpow(int x, int y, int m = mod) {
  int res = 1;
  while (y) {
    if (y % 2) {
      res *= x;
      res %= m;
    }
    x = x * x % m;
    y /= 2;
  }
  return res;
}

int mypow(int x, int y) {
  int res = 1;
  while (y) {
    if (y % 2) {
      res *= x;
    }
    x = x * x;
    y /= 2;
  }
  return res;
}
// is the number (x) a prime number?
bool prime(int x) {
  for (int i = 2; i * i <= x; i++) {
    if (!(x % i)) {
      return false;
    }
  }
  return true;
}

// saidai-kouyakusuu
inline int gcd(int x, int y) {
  if (!y) {
    return x;
  }
  return gcd(y, x % y);
}

// number of keta
int keta(int x) {
  int ans = 0;
  while (x) {
    x /= 10;
    ans++;
  }
  return ans;
}

// sum of keta
int ketasum(int x) {
  int ans = 0;
  while (x) {
    ans += x % 10;
    x /= 10;
  }
  return ans;
}

inline int lcm(int x, int y) {
  int ans = x / gcd(x, y) * y;
  return ans;
}
int twobeki(int x) {
  int ans = 0;
  while (1) {
    if (!(x & 1)) {
      ans++;
      x /= 2;
    } else {
      break;
    }
  }
  return ans;
}

template <class T, class U> inline bool chmax(T &lhs, const U &rhs) {
  if (lhs < rhs) {
    lhs = rhs;
    return 1;
  }
  return 0;
}
template <class T, class U> inline bool chmin(T &lhs, const U &rhs) {
  if (lhs > rhs) {
    lhs = rhs;
    return 1;
  }
  return 0;
}
void Yes() { cout << "Yes" << endl; }
void No() { cout << "No" << endl; }
void YES() { cout << "YES" << endl; }
void NO() { cout << "NO" << endl; }

int kai(int x, int y) {
  int res = 1;
  for (int i = x - y + 1; i <= x; i++) {
    res *= i;
    res %= mod;
  }
  return res;
}

int comb(int x, int y) {
  if (y > x)
    return 0;
  return kai(x, y) * modpow(kai(y, y), mod - 2) % mod;
}

#define fin(i) scanf("%lld", &i)
#define fout(i) printf("%lld", i)
#define fendl printf("\\n")
// Library-End

class modInt {
  int value, modulo;

public:
  modInt() : value(0), modulo(mod) { value = 0; }
  template <typename T>
  modInt(T value = 0, int modulo = mod) : value(value), modulo(modulo) {
    if (value < 0) {
      value = -value;
      value %= modulo;
      value = -value;
      value += modulo;
    }
    this->value = value % modulo;
  }
  inline operator int() const { return value; }
  inline modInt &operator+=(modInt x) {
    value += x.value;
    if (value >= modulo)
      value -= modulo;
    return *this;
  }
  inline modInt &operator++() {
    if (value == modulo - 1)
      value = 0;
    else
      value++;
    return *this;
  }
  inline modInt &operator-() const { return modInt(0) -= *this; }
  inline modInt &operator-=(modInt x) {
    value -= x.value;
    if (value < 0)
      value += modulo;
    return *this;
  }
  inline modInt &operator--() {
    if (value == 0)
      value = modulo - 1;
    else
      value--;
    return *this;
  }
  inline modInt &operator*=(modInt x) {
    value = value * x.value % modulo;
    return *this;
  }
  inline modInt &operator/=(modInt x) { return operator*=(x.inv()); }
  inline modInt inv() { return modpow(*this, modulo - 2); }
  template <typename T> modInt operator+(T x) { return modInt(*this) += x; }
  template <typename T> modInt &operator+=(T x) {
    return operator+=(modInt(x, modulo));
  }
  template <typename T> modInt operator-(T x) { return modInt(*this) -= x; }
  template <typename T> modInt &operator-=(T x) {
    return operator-=(modInt(x, modulo));
  }
  template <typename T> modInt operator*(T x) { return modInt(*this) *= x; }
  template <typename T> modInt &operator*=(T x) {
    return operator*=(modInt(x, modulo));
  }
  template <typename T> modInt operator/(T x) { return modInt(*this) /= x; }
  template <typename T> modInt &operator/=(T x) {
    return operator/=(modInt(x, modulo));
  }
};
istream &operator>>(istream &ist, modInt &x) {
  int a;
  ist >> a;
  x = a;
  return ist;
}
#define vecin(v)                                                               \\
  for (int i = 0; i < v.size(); i++)                                           \\
    scanf("%lld", &v[i]);
#define vecout(v)                                                              \\
  {                                                                            \\
    for (int i = 0; i < v.size(); i++)                                         \\
      printf("%lld\\n", v[i]);                                                  \\
  }
#define endl "\\n" // interactive の時に注意！！！
// SegTree
template <class T> class SegTree {
  int n;                       // 葉の数
  vector<T> data;              // データを格納するvector
  T def;                       // 初期値かつ単位元
  function<T(T, T)> operation; // 区間クエリで使う処理
  function<T(T, T)> update;    // 点更新で使う処理

  // 区間[a,b)の総和。ノードk=[l,r)に着目している。
  T _query(int a, int b, int k, int l, int r) {
    if (r <= a || b <= l)
      return def; // 交差しない
    if (a <= l && r <= b)
      return data[k]; // a,l,r,bの順で完全に含まれる
    else {
      T c1 = _query(a, b, 2 * k + 1, l, (l + r) / 2); // 左の子
      T c2 = _query(a, b, 2 * k + 2, (l + r) / 2, r); // 右の子
      return operation(c1, c2);
    }
  }

public:
  // _n:必要サイズ, _def:初期値かつ単位元, _operation:クエリ関数,
  // _update:更新関数
  SegTree(size_t _n, T _def, function<T(T, T)> _operation,
          function<T(T, T)> _update)
      : def(_def), operation(_operation), update(_update) {
    n = 1;
    while (n < _n) {
      n *= 2;
    }
    data = vector<T>(2 * n - 1, def);
  }

  // 場所i(0-indexed)の値をxで更新
  void change(int i, T x) {
    i += n - 1;
    data[i] = update(data[i], x);
    while (i > 0) {
      i = (i - 1) / 2;
      data[i] = operation(data[i * 2 + 1], data[i * 2 + 2]);
    }
  }

  // [a, b)の区間クエリを実行
  T query(int a, int b) { return _query(a, b, 0, 0, n); }

  // 添字でアクセス
  T operator[](int i) { return data[i + n - 1]; }
};

#define R_MIN ([](long long a, long long b) { return min(a, b); })
#define R_MAX ([](long long a, long long b) { return max(a, b); })
#define R_SUM ([](long long a, long long b) { return a + b; })

#define NORMAL_UPDATE ([](long long a, long long b) { return b; })
#define ADD_UPDATE ([](long long a, long long b) { return a + b; })
#define MINUS_UPDATE ([](long long a, long long b) { return a - b; }

class Union_Find {
  vector<int> par;
  vector<int> rankmy;
  vector<int> ookisa;

public:
  Union_Find(int size) {
    par = vector<int>(size);
    rankmy = vector<int>(size);
    ookisa = vector<int>(size);
    for (int i = 0; i < size; i++) {
      par[i] = i;
      ookisa[i] = 1;
    }
  }

  int find(int x) {
    if (par[x] == x) {
      return x;
    }
    return par[x] = find(par[x]);
  }

  void unite(int x, int y) {
    x = find(x);
    y = find(y);
    if (x == y) {
      return;
    }
    if (rankmy[x] < rankmy[y]) {
      par[x] = y;
      ookisa[y] += ookisa[x];
      ookisa[x] = 0;
    } else {
      par[y] = x;
      ookisa[x] += ookisa[y];
      ookisa[y] = 0;
      if (rankmy[x] == rankmy[y]) {
        rankmy[x]++;
      }
    }
  }
  int size(int i) {
    i = find(i);
    return ookisa[i];
  }
  bool same(int x, int y) { return find(x) == find(y); }
};

// Union-Find-End

int n, k, a[200004], ans;
set<P> s;
P b[200004];
signed main() {
  ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  cin >> n;
  rep(i, n) {
    cin >> a[i];
    b[i] = {a[i], i};
  }
  sort(b, b + n, greater<P>());
  ans = 0 - inf;
  rep(i, n) {
    bool dame[200004];
    memset(dame, 0, sizeof(dame));
    int now = 0;
    int ka = 0;
    dame[i] = 1;
    for (int j = 0; j < n; j++) {
      if (now == n / 2) {
        break;
      }
      if (!dame[b[j].second]) {
        ka += b[j].first;
        dame[b[j].second + 1] = 1;
        dame[b[j].second] = 1;
        if (b[j].second)
          dame[b[j].second - 1] = 1;
        now++;
      }
    }
    if (now == n / 2)
      chmax(ans, ka);
  }
  cout << ans << endl;
}