Problem p03171 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>

using namespace std;

#define int long long
#define double long double
#define FOR(i, a, b) for (ll i = (a); i < (b); ++i)
#define FORR(i, a, b) for (ll i = (a); i > (b); --i)
#define REP(i, n) for (ll i = 0; i < (n); ++i)
#define REPR(i, n) for (ll i = n; i >= 0; i--)
#define FOREACH(x, a) for (auto &(x) : (a))
#define VECCIN(x)                                                              \
  for (auto &youso_ : (x))                                                     \
  cin >> youso_
#define bitcnt __builtin_popcount
#define SZ(x) ((ll)(x).size())
#define fi first
#define se second
#define All(a) (a).begin(), (a).end()
template <typename T = long long> inline T IN() {
  T x;
  cin >> x;
  return (x);
}
inline void CIN() {}
template <class Head, class... Tail>
inline void CIN(Head &&head, Tail &&...tail) {
  cin >> head;
  CIN(move(tail)...);
}
#define CCIN(...)                                                              \
  char __VA_ARGS__;                                                            \
  CIN(__VA_ARGS__)
#define DCIN(...)                                                              \
  double __VA_ARGS__;                                                          \
  CIN(__VA_ARGS__)
#define LCIN(...)                                                              \
  ll __VA_ARGS__;                                                              \
  CIN(__VA_ARGS__)
#define SCIN(...)                                                              \
  string __VA_ARGS__;                                                          \
  CIN(__VA_ARGS__)
#define Printv(v)                                                              \
  {                                                                            \
    REP(x, v.size()) { cout << v[x] << (x == v.size() - 1 ? "\n" : " "); }     \
  }
template <typename T = string> inline void eputs(T s) {
  cout << s << "\n";
  exit(0);
}
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
  std::fill((T *)array, (T *)(array + N), val);
}
template <typename T> using PQG = priority_queue<T, vector<T>, greater<T>>;
template <typename T> using PQ = priority_queue<T>;

typedef long long ll;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef pair<ll, ll> PL;

const int INF = 1e9;
const int MOD = 1e9 + 7;
const double PI = atan(1.0) * 4.0;
const ll LINF = 1e18;
const ll dx[] = {1, 0, -1, 0};
const ll dy[] = {0, 1, 0, -1};

void cinfast() {
  cin.tie(0);
  ios::sync_with_stdio(false);
}

ll N, K;
ll dp[3000][3000];
ll a[3000];

signed main() {
  cin >> N;
  REP(i, N) cin >> a[i];
  REPR(i, N - 1) {
    FOR(j, i, N) {
      if ((N - i - j - 1) % 2 == 0) {
        dp[i][j] = max(dp[i + 1][j] + a[i], dp[i][j - 1] + a[j]);
      } else {
        dp[i][j] = min(dp[i + 1][j] - a[i], dp[i][j - 1] - a[j]);
      }
    }
  }
  cout << dp[0][N - 1] << "\n";
}


Fixed submission:
#include <bits/stdc++.h>

using namespace std;

#define int long long
#define double long double
#define FOR(i, a, b) for (ll i = (a); i < (b); ++i)
#define FORR(i, a, b) for (ll i = (a); i > (b); --i)
#define REP(i, n) for (ll i = 0; i < (n); ++i)
#define REPR(i, n) for (ll i = n; i >= 0; i--)
#define FOREACH(x, a) for (auto &(x) : (a))
#define VECCIN(x)                                                              \
  for (auto &youso_ : (x))                                                     \
  cin >> youso_
#define bitcnt __builtin_popcount
#define SZ(x) ((ll)(x).size())
#define fi first
#define se second
#define All(a) (a).begin(), (a).end()
template <typename T = long long> inline T IN() {
  T x;
  cin >> x;
  return (x);
}
inline void CIN() {}
template <class Head, class... Tail>
inline void CIN(Head &&head, Tail &&...tail) {
  cin >> head;
  CIN(move(tail)...);
}
#define CCIN(...)                                                              \
  char __VA_ARGS__;                                                            \
  CIN(__VA_ARGS__)
#define DCIN(...)                                                              \
  double __VA_ARGS__;                                                          \
  CIN(__VA_ARGS__)
#define LCIN(...)                                                              \
  ll __VA_ARGS__;                                                              \
  CIN(__VA_ARGS__)
#define SCIN(...)                                                              \
  string __VA_ARGS__;                                                          \
  CIN(__VA_ARGS__)
#define Printv(v)                                                              \
  {                                                                            \
    REP(x, v.size()) { cout << v[x] << (x == v.size() - 1 ? "\n" : " "); }     \
  }
template <typename T = string> inline void eputs(T s) {
  cout << s << "\n";
  exit(0);
}
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
  std::fill((T *)array, (T *)(array + N), val);
}
template <typename T> using PQG = priority_queue<T, vector<T>, greater<T>>;
template <typename T> using PQ = priority_queue<T>;

typedef long long ll;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef pair<ll, ll> PL;

const int INF = 1e9;
const int MOD = 1e9 + 7;
const double PI = atan(1.0) * 4.0;
const ll LINF = 1e18;
const ll dx[] = {1, 0, -1, 0};
const ll dy[] = {0, 1, 0, -1};

void cinfast() {
  cin.tie(0);
  ios::sync_with_stdio(false);
}

ll N, K;
ll dp[3001][3001];
ll a[3001];

signed main() {
  cin >> N;
  REP(i, N) cin >> a[i];
  REPR(i, N - 1) {
    FOR(j, i, N) {
      if ((N - i - j - 1) % 2 == 0) {
        dp[i][j] = max(dp[i + 1][j] + a[i], dp[i][j - 1] + a[j]);
      } else {
        dp[i][j] = min(dp[i + 1][j] - a[i], dp[i][j - 1] - a[j]);
      }
    }
  }
  cout << dp[0][N - 1] << "\n";
}