Problem p02716 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
#include <boost/multiprecision/cpp_int.hpp>
using namespace std;
using namespace boost::multiprecision;

#define REP(i, n) for (int i = 0; i < (n); ++i)
#define rep(i, a, b) for (int i = a; i < (b); ++i)
#define all(v) v.begin(), v.end()
#define showVector(v)                                                          \\
  REP(i, v.size()) { cout << (v[i]) << " "; }                                  \\
  cout << endl;
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
typedef long long int ll;
typedef pair<ll, ll> P_ii;
typedef pair<double, double> P_dd;

template <class T> using MaxHeap = std::priority_queue<T>;

template <class T>
using MinHeap = std::priority_queue<T, std::vector<T>, std::greater<T>>;

template <class T> vector<T> make_vec(size_t a) { return vector<T>(a); }

template <class T, class... Ts> auto make_vec(size_t a, Ts... ts) {
  return vector<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...));
}

template <typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type fill_v(T &t, const V &v) {
  t = v;
}

template <typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type fill_v(T &t, const V &v) {
  for (auto &e : t)
    fill_v(e, v);
}

int pop_count(int n) { return __builtin_popcount(n); }

int pop_count(ll n) { return __builtin_popcountll(n); }

ll gcd(ll a, ll b) {
  if (a < b)
    swap(a, b);

  if (b == 0)
    return a;
  return gcd(b, a % b);
}

ll lcm(ll a, ll b) {
  ll g = gcd(a, b);
  return (a / g) * b;
}

// 素数判定 O(√n)
bool is_prime(ll n) {
  if (n == 1)
    return false;
  for (ll i = 2; i * i <= n; i++) {
    if (n % i == 0)
      return false;
  }
  return true;
}

// 約数列挙 O(√n)
vector<ll> divisor(ll n) {
  vector<ll> res;
  for (ll i = 1; i * i <= n; i++) {
    if (n % i == 0) {
      res.push_back(i);
      if (i != n / i)
        res.push_back(n / i);
    }
  }
  return res;
}

template <typename T> map<T, ll> prime_factorize(T x) {
  map<T, ll> res;
  for (int i = 2; i * i <= x; i++) {
    while (x % i == 0) {
      x /= i;
      res[i]++;
    }
  }
  if (x != 1)
    res[x]++;
  return res;
}

// エラトステネスの篩
// return lp[i] := iの最小素因数(lp[i] == iならば素数)
vector<int> SieveOfEratosthenes(int N = 10000000) {
  vector<int> lp(N + 1, 0);
  vector<int> pr;
  for (int i = 2; i <= N; ++i) {
    if (lp[i] == 0) {
      lp[i] = i;
      pr.push_back(i);
    }
    for (int j = 0; j < (int)pr.size() && pr[j] <= lp[i] && i * pr[j] <= N; ++j)
      lp[i * pr[j]] = pr[j];
  }
  return lp;
}

// auto mod int
// https://youtu.be/L8grWxBlIZ4?t=9858
// https://youtu.be/ERZuLAxZffQ?t=4807 : optimize
// https://youtu.be/8uowVvQ_-Mo?t=1329 : division
const int mod = 1000000007;
struct mint {
  ll x; // typedef long long ll;
  mint(ll x = 0) : x(x % mod) {}
  mint &operator+=(const mint a) {
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const {
    mint res(*this);
    return res += a;
  }
  mint operator-(const mint a) const {
    mint res(*this);
    return res -= a;
  }
  mint operator*(const mint a) const {
    mint res(*this);
    return res *= a;
  }
  mint pow(ll t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return (*this) *= a.inv(); }
  mint operator/(const mint a) const {
    mint res(*this);
    return res /= a;
  }
};

const int MOD = 1000000007;
const int inf = 1e9 + 7;
const ll longinf = 1LL << 60;

ll intceil(ll a, ll b) {
  if (a < 0) {
    a *= -1;
    b *= -1;
  }
  if (b >= 0)
    return (a + b - 1) / b;
  return a / b;
}

ll intfloor(ll a, ll b) {
  if (a < 0) {
    a *= -1;
    b *= -1;
  }
  if (b >= 0)
    return a / b;
  return (a - b + 1) / b;
}

void addM(ll &a, ll b) {
  a += b;
  if (a >= MOD)
    a -= MOD;
}

void mulM(ll &a, ll b) { a = ((a % MOD) * (b % MOD)) % MOD; }

ll powM(ll a, ll b) {
  ll ret = 1;
  ll tmp = a;
  while (b > 0) {
    if ((b & 1) == 1)
      ret = (ret * tmp) % MOD;
    tmp = (tmp * tmp) % MOD;
    b = b >> 1;
  }
  return ret;
}

// mod. m での a の逆元 a^{-1} を計算する
ll modinv(ll a, ll m) {
  ll b = m, u = 1, v = 0;
  while (b) {
    ll t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0)
    u += m;
  return u;
}

// ラングレンス圧縮
vector<pair<char, int>> rang_com(string s) {
  vector<pair<char, int>> ret;
  string t = s;
  t.erase(unique(all(t)), t.end());
  int now = 0;
  int pre = 0;
  for (auto ct : t) {
    while (now < s.size() && s[now] == ct)
      now++;
    if (ret.size() == 0) {
      ret.push_back({ct, now});
    } else {
      ret.push_back({ct, now - pre});
    }
    pre = now;
  }
  return ret;
}

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int N;
  cin >> N;

  vector<ll> a(N);
  REP(i, N) cin >> a[i];

  auto dp = make_vec<ll>(N + 1, 4);
  fill_v(dp, -longinf);
  dp[0][0] = 0;

  int k = 1 + N % 2;
  REP(i, N) {
    REP(j, k + 1) {
      chmax(dp[i + 1][j + 1], dp[i][j]);
      ll now = dp[i][j];
      if ((i + j) % 2 == 0)
        now += a[i];
      chmax(dp[i + 1][j], now);
    }
  }
  cout << dp[N][k] << endl;

  return 0;
}

Error: 0

Fixed submission:

#include <bits/stdc++.h>
#include <boost/multiprecision/cpp_int.hpp>
using namespace std;
using namespace boost::multiprecision;

#define REP(i, n) for (int i = 0; i < (n); ++i)
#define rep(i, a, b) for (int i = a; i < (b); ++i)
#define all(v) v.begin(), v.end()
#define showVector(v)                                                          \\
  REP(i, v.size()) { cout << (v[i]) << " "; }                                  \\
  cout << endl;
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
typedef long long int ll;
typedef pair<ll, ll> P_ii;
typedef pair<double, double> P_dd;

template <class T> using MaxHeap = std::priority_queue<T>;

template <class T>
using MinHeap = std::priority_queue<T, std::vector<T>, std::greater<T>>;

template <class T> vector<T> make_vec(size_t a) { return vector<T>(a); }

template <class T, class... Ts> auto make_vec(size_t a, Ts... ts) {
  return vector<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...));
}

template <typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type fill_v(T &t, const V &v) {
  t = v;
}

template <typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type fill_v(T &t, const V &v) {
  for (auto &e : t)
    fill_v(e, v);
}

int pop_count(int n) { return __builtin_popcount(n); }

int pop_count(ll n) { return __builtin_popcountll(n); }

ll gcd(ll a, ll b) {
  if (a < b)
    swap(a, b);

  if (b == 0)
    return a;
  return gcd(b, a % b);
}

ll lcm(ll a, ll b) {
  ll g = gcd(a, b);
  return (a / g) * b;
}

// 素数判定 O(√n)
bool is_prime(ll n) {
  if (n == 1)
    return false;
  for (ll i = 2; i * i <= n; i++) {
    if (n % i == 0)
      return false;
  }
  return true;
}

// 約数列挙 O(√n)
vector<ll> divisor(ll n) {
  vector<ll> res;
  for (ll i = 1; i * i <= n; i++) {
    if (n % i == 0) {
      res.push_back(i);
      if (i != n / i)
        res.push_back(n / i);
    }
  }
  return res;
}

template <typename T> map<T, ll> prime_factorize(T x) {
  map<T, ll> res;
  for (int i = 2; i * i <= x; i++) {
    while (x % i == 0) {
      x /= i;
      res[i]++;
    }
  }
  if (x != 1)
    res[x]++;
  return res;
}

// エラトステネスの篩
// return lp[i] := iの最小素因数(lp[i] == iならば素数)
vector<int> SieveOfEratosthenes(int N = 10000000) {
  vector<int> lp(N + 1, 0);
  vector<int> pr;
  for (int i = 2; i <= N; ++i) {
    if (lp[i] == 0) {
      lp[i] = i;
      pr.push_back(i);
    }
    for (int j = 0; j < (int)pr.size() && pr[j] <= lp[i] && i * pr[j] <= N; ++j)
      lp[i * pr[j]] = pr[j];
  }
  return lp;
}

// auto mod int
// https://youtu.be/L8grWxBlIZ4?t=9858
// https://youtu.be/ERZuLAxZffQ?t=4807 : optimize
// https://youtu.be/8uowVvQ_-Mo?t=1329 : division
const int mod = 1000000007;
struct mint {
  ll x; // typedef long long ll;
  mint(ll x = 0) : x(x % mod) {}
  mint &operator+=(const mint a) {
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const {
    mint res(*this);
    return res += a;
  }
  mint operator-(const mint a) const {
    mint res(*this);
    return res -= a;
  }
  mint operator*(const mint a) const {
    mint res(*this);
    return res *= a;
  }
  mint pow(ll t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return (*this) *= a.inv(); }
  mint operator/(const mint a) const {
    mint res(*this);
    return res /= a;
  }
};

const int MOD = 1000000007;
const int inf = 1e9 + 7;
const ll longinf = 1LL << 60;

ll intceil(ll a, ll b) {
  if (a < 0) {
    a *= -1;
    b *= -1;
  }
  if (b >= 0)
    return (a + b - 1) / b;
  return a / b;
}

ll intfloor(ll a, ll b) {
  if (a < 0) {
    a *= -1;
    b *= -1;
  }
  if (b >= 0)
    return a / b;
  return (a - b + 1) / b;
}

void addM(ll &a, ll b) {
  a += b;
  if (a >= MOD)
    a -= MOD;
}

void mulM(ll &a, ll b) { a = ((a % MOD) * (b % MOD)) % MOD; }

ll powM(ll a, ll b) {
  ll ret = 1;
  ll tmp = a;
  while (b > 0) {
    if ((b & 1) == 1)
      ret = (ret * tmp) % MOD;
    tmp = (tmp * tmp) % MOD;
    b = b >> 1;
  }
  return ret;
}

// mod. m での a の逆元 a^{-1} を計算する
ll modinv(ll a, ll m) {
  ll b = m, u = 1, v = 0;
  while (b) {
    ll t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0)
    u += m;
  return u;
}

// ラングレンス圧縮
vector<pair<char, int>> rang_com(string s) {
  vector<pair<char, int>> ret;
  string t = s;
  t.erase(unique(all(t)), t.end());
  int now = 0;
  int pre = 0;
  for (auto ct : t) {
    while (now < s.size() && s[now] == ct)
      now++;
    if (ret.size() == 0) {
      ret.push_back({ct, now});
    } else {
      ret.push_back({ct, now - pre});
    }
    pre = now;
  }
  return ret;
}

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int N;
  cin >> N;

  vector<ll> a(N);
  REP(i, N) cin >> a[i];

  auto dp = make_vec<ll>(N + 1, 3);
  fill_v(dp, -longinf);
  dp[0][0] = 0;

  int k = 1 + N % 2;
  REP(i, N) {
    REP(j, k + 1) {
      chmax(dp[i + 1][j + 1], dp[i][j]);
      ll now = dp[i][j];
      if ((i + j) % 2 == 0)
        now += a[i];
      chmax(dp[i + 1][j], now);
    }
  }
  cout << dp[N][k] << endl;

  return 0;
}