Problem p03171 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
#define ff first
#define ss second
#define int long long
#define rep(i, n) for (int i = 0; i < n; i++)

#define n_l '\n'
template <typename T, size_t N> int SIZE(const T (&t)[N]) { return N; }
template <typename T> int SIZE(const T &t) { return t.size(); }
string to_string(const string s, int x1 = 0, int x2 = 1e9) {
  return '"' + ((x1 < s.size()) ? s.substr(x1, x2 - x1 + 1) : "") + '"';
}
string to_string(const char *s) { return to_string((string)s); }
string to_string(const bool b) { return (b ? "true" : "false"); }
string to_string(const char c) { return string({c}); }
template <size_t N>
string to_string(const bitset<N> &b, int x1 = 0, int x2 = 1e9) {
  string t = "";
  for (int __iii__ = min(x1, SIZE(b)), __jjj__ = min(x2, SIZE(b) - 1);
       __iii__ <= __jjj__; ++__iii__) {
    t += b[__iii__] + '0';
  }
  return '"' + t + '"';
}
template <typename A, typename... C>
string to_string(const A(&v), int x1 = 0, int x2 = 1e9, C... coords);
int l_v_l_v_l = 0, t_a_b_s = 0;
template <typename A, typename B> string to_string(const pair<A, B> &p) {
  l_v_l_v_l++;
  string res = "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
  l_v_l_v_l--;
  return res;
}
template <typename A, typename... C>
string to_string(const A(&v), int x1, int x2, C... coords) {
  int rnk = rank<A>::value;
  string tab(t_a_b_s, ' ');
  string res = "";
  bool first = true;
  if (l_v_l_v_l == 0)
    res += n_l;
  res += tab + "[";
  x1 = min(x1, SIZE(v)), x2 = min(x2, SIZE(v));
  auto l = begin(v);
  advance(l, x1);
  auto r = l;
  advance(r, (x2 - x1) + (x2 < SIZE(v)));
  for (auto e = l; e != r; e = next(e)) {
    if (!first) {
      res += ", ";
    }
    first = false;
    l_v_l_v_l++;
    if (e != l) {
      if (rnk > 1) {
        res += n_l;
        t_a_b_s = l_v_l_v_l;
      };
    } else {
      t_a_b_s = 0;
    }
    res += to_string(*e, coords...);
    l_v_l_v_l--;
  }
  res += "]";
  if (l_v_l_v_l == 0)
    res += n_l;
  return res;
}
void dbgm() { ; }
template <typename Heads, typename... Tails> void dbgm(Heads H, Tails... T) {
  cout << to_string(H) << " | ";
  dbgm(T...);
}
#define dbg(...)                                                               \
  cout << "[" << #__VA_ARGS__ << "]: ";                                        \
  dbgm(__VA_ARGS__);                                                           \
  cout << endl

int32_t main() {
#ifndef ONLINE_JUDGE
  freopen("inp.txt", "r", stdin);
  freopen("outp.txt", "w", stdout);
#endif
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);

  int n, sum = 0;
  cin >> n;
  vector<int> a(n + 1);
  for (int i = 1; i <= n; i++)
    cin >> a[i];
  vector<vector<int>> dp(n + 1, vector<int>(n + 1));

  for (int i = 1; i <= n; i++) {
    dp[i][i] = a[i];
    sum += a[i];
  }
  for (int len = 2; len <= n; len++) {
    for (int i = 1; i <= n - len + 1; i++) {
      int j = i + len - 1;
      dp[i][j] = max(a[i] - dp[i + 1][j], a[j] - dp[i][j - 1]);
    }
  }

  cout << dp[1][n] << '\n';

  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#define ff first
#define ss second
#define int long long
#define rep(i, n) for (int i = 0; i < n; i++)

#define n_l '\n'
template <typename T, size_t N> int SIZE(const T (&t)[N]) { return N; }
template <typename T> int SIZE(const T &t) { return t.size(); }
string to_string(const string s, int x1 = 0, int x2 = 1e9) {
  return '"' + ((x1 < s.size()) ? s.substr(x1, x2 - x1 + 1) : "") + '"';
}
string to_string(const char *s) { return to_string((string)s); }
string to_string(const bool b) { return (b ? "true" : "false"); }
string to_string(const char c) { return string({c}); }
template <size_t N>
string to_string(const bitset<N> &b, int x1 = 0, int x2 = 1e9) {
  string t = "";
  for (int __iii__ = min(x1, SIZE(b)), __jjj__ = min(x2, SIZE(b) - 1);
       __iii__ <= __jjj__; ++__iii__) {
    t += b[__iii__] + '0';
  }
  return '"' + t + '"';
}
template <typename A, typename... C>
string to_string(const A(&v), int x1 = 0, int x2 = 1e9, C... coords);
int l_v_l_v_l = 0, t_a_b_s = 0;
template <typename A, typename B> string to_string(const pair<A, B> &p) {
  l_v_l_v_l++;
  string res = "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
  l_v_l_v_l--;
  return res;
}
template <typename A, typename... C>
string to_string(const A(&v), int x1, int x2, C... coords) {
  int rnk = rank<A>::value;
  string tab(t_a_b_s, ' ');
  string res = "";
  bool first = true;
  if (l_v_l_v_l == 0)
    res += n_l;
  res += tab + "[";
  x1 = min(x1, SIZE(v)), x2 = min(x2, SIZE(v));
  auto l = begin(v);
  advance(l, x1);
  auto r = l;
  advance(r, (x2 - x1) + (x2 < SIZE(v)));
  for (auto e = l; e != r; e = next(e)) {
    if (!first) {
      res += ", ";
    }
    first = false;
    l_v_l_v_l++;
    if (e != l) {
      if (rnk > 1) {
        res += n_l;
        t_a_b_s = l_v_l_v_l;
      };
    } else {
      t_a_b_s = 0;
    }
    res += to_string(*e, coords...);
    l_v_l_v_l--;
  }
  res += "]";
  if (l_v_l_v_l == 0)
    res += n_l;
  return res;
}
void dbgm() { ; }
template <typename Heads, typename... Tails> void dbgm(Heads H, Tails... T) {
  cout << to_string(H) << " | ";
  dbgm(T...);
}
#define dbg(...)                                                               \
  cout << "[" << #__VA_ARGS__ << "]: ";                                        \
  dbgm(__VA_ARGS__);                                                           \
  cout << endl

int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);

  int n, sum = 0;
  cin >> n;
  vector<int> a(n + 1);
  for (int i = 1; i <= n; i++)
    cin >> a[i];
  vector<vector<int>> dp(n + 1, vector<int>(n + 1));

  for (int i = 1; i <= n; i++) {
    dp[i][i] = a[i];
    sum += a[i];
  }
  for (int len = 2; len <= n; len++) {
    for (int i = 1; i <= n - len + 1; i++) {
      int j = i + len - 1;
      dp[i][j] = max(a[i] - dp[i + 1][j], a[j] - dp[i][j - 1]);
    }
  }

  cout << dp[1][n] << '\n';

  return 0;
}