Problem p03171 (C++)

Buggy submission (status: Runtime Error):
#define _CRT_SECURE_NO_WARNINGS

#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <functional>
#include <iostream>
#include <iterator>
#include <limits>
#include <map>
#include <memory>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;
#define FOR(i, n) for (int i = 0; i < (n); i++)
#define sz(c) ((int)c.size())
#define ten(n) ((int)1e##n)
using ll = long long;
using Pii = pair<int, int>;
using Pll = pair<ll, ll>;

template <typename...> static inline int getchar_unlocked(void) {
  return getchar();
}
template <typename...> static inline void putchar_unlocked(int c) {
  putchar(c);
}
#define mygc(c) (c) = getchar_unlocked()
#define mypc(c) putchar_unlocked(c)
void reader(int &x) {
  int k, m = 0;
  x = 0;
  for (;;) {
    mygc(k);
    if (k == '-') {
      m = 1;
      break;
    }
    if ('0' <= k && k <= '9') {
      x = k - '0';
      break;
    }
  }
  for (;;) {
    mygc(k);
    if (k < '0' || k > '9')
      break;
    x = x * 10 + k - '0';
  }
  if (m)
    x = -x;
}
void reader(ll &x) {
  int k, m = 0;
  x = 0;
  for (;;) {
    mygc(k);
    if (k == '-') {
      m = 1;
      break;
    }
    if ('0' <= k && k <= '9') {
      x = k - '0';
      break;
    }
  }
  for (;;) {
    mygc(k);
    if (k < '0' || k > '9')
      break;
    x = x * 10 + k - '0';
  }
  if (m)
    x = -x;
}
int reader(char c[]) {
  int i, s = 0;
  for (;;) {
    mygc(i);
    if (i != ' ' && i != '\n' && i != '\r' && i != '\t' && i != EOF)
      break;
  }
  c[s++] = i;
  for (;;) {
    mygc(i);
    if (i == ' ' || i == '\n' || i == '\r' || i == '\t' || i == EOF)
      break;
    c[s++] = i;
  }
  c[s] = '\0';
  return s;
}
int reader(string &c) {
  int i;
  for (;;) {
    mygc(i);
    if (i != ' ' && i != '\n' && i != '\r' && i != '\t' && i != EOF)
      break;
  }
  c.push_back(i);
  for (;;) {
    mygc(i);
    if (i == ' ' || i == '\n' || i == '\r' || i == '\t' || i == EOF)
      break;
    c.push_back(i);
  };
  return sz(c);
}
template <class T, class S> void reader(T &x, S &y) {
  reader(x);
  reader(y);
}
template <class T, class S, class U> void reader(T &x, S &y, U &z) {
  reader(x);
  reader(y);
  reader(z);
}
template <class T, class S, class U, class V>
void reader(T &x, S &y, U &z, V &w) {
  reader(x);
  reader(y);
  reader(z);
  reader(w);
}
void writer(int x, char c) {
  int s = 0, m = 0;
  char f[10];
  if (x < 0)
    m = 1, x = -x;
  while (x)
    f[s++] = x % 10, x /= 10;
  if (!s)
    f[s++] = 0;
  if (m)
    mypc('-');
  while (s--)
    mypc(f[s] + '0');
  mypc(c);
}
void writer(ll x, char c) {
  int s = 0, m = 0;
  char f[20];
  if (x < 0)
    m = 1, x = -x;
  while (x)
    f[s++] = x % 10, x /= 10;
  if (!s)
    f[s++] = 0;
  if (m)
    mypc('-');
  while (s--)
    mypc(f[s] + '0');
  mypc(c);
}
void writer(const char c[]) {
  int i;
  for (i = 0; c[i] != '\0'; i++)
    mypc(c[i]);
}
void writer(const string &x, char c) {
  int i;
  for (i = 0; x[i] != '\0'; i++)
    mypc(x[i]);
  mypc(c);
}
void writer(const char x[], char c) {
  int i;
  for (i = 0; x[i] != '\0'; i++)
    mypc(x[i]);
  mypc(c);
}
template <class T> void writerLn(T x) { writer(x, '\n'); }
template <class T, class S> void writerLn(T x, S y) {
  writer(x, ' ');
  writer(y, '\n');
}
template <class T, class S, class U> void writerLn(T x, S y, U z) {
  writer(x, ' ');
  writer(y, ' ');
  writer(z, '\n');
}
template <class T, class S, class U, class V>
void writerLn(T x, S y, U z, V v) {
  writer(x, ' ');
  writer(y, ' ');
  writer(z, ' ');
  writer(v, '\n');
}
template <class T> void writerArr(T x[], int n) {
  if (!n) {
    mypc('\n');
    return;
  }
  FOR(i, n - 1) writer(x[i], ' ');
  writer(x[n - 1], '\n');
}
template <class T> void writerArr(vector<T> &x) {
  writerArr(x.data(), (int)x.size());
}

template <class T> void chmin(T &a, const T &b) {
  if (a > b)
    a = b;
}
template <class T> void chmax(T &a, const T &b) {
  if (a < b)
    a = b;
}

template <class T> T gcd(T a, T b) { return b ? gcd(b, a % b) : a; }
template <class T> T lcm(T a, T b) { return a / gcd(a, b) * b; }
ll mod_pow(ll a, ll n, ll mod) {
  ll ret = 1;
  ll p = a % mod;
  while (n) {
    if (n & 1)
      ret = ret * p % mod;
    p = p * p % mod;
    n >>= 1;
  }
  return ret;
}
template <class T> T extgcd(T a, T b, T &x, T &y) {
  for (T u = y = 1, v = x = 0; a;) {
    T q = b / a;
    swap(x -= q * u, u);
    swap(y -= q * v, v);
    swap(b -= q * a, a);
  }
  return b;
}
ll mod_inv(ll a, ll m) {
  ll x, y;
  extgcd<ll>(a, m, x, y);
  return (m + x % m) % m;
}

#ifdef _DEBUG
template <typename... Args>
void debugPrintf(const char *format, Args const &...args) {
  fprintf(stdout, format, args...);
  fflush(stdout);
}
#else
#define debugPrintf(...)
#endif

ll a[100];
ll memo[3001][3001][2];

ll dfs(int l, int r, bool f) {
  ll &ret = memo[l][r][f];
  if (ret != 0x8f8f8f8f8f8f8f8f)
    return ret;
  if (l == r)
    return ret = 0;

  if (f) {
    ll l1 = dfs(l + 1, r, !f) + a[l];
    ll l2 = dfs(l, r - 1, !f) + a[r - 1];
    return ret = max(l1, l2);
  } else {
    ll l1 = dfs(l + 1, r, !f) - a[l];
    ll l2 = dfs(l, r - 1, !f) - a[r - 1];
    return ret = min(l1, l2);
  }
}

int main() {
  int n;
  reader(n);
  FOR(i, n) reader(a[i]);
  memset(memo, 0x8f, sizeof(memo));
  ll ans = dfs(0, n, true);
  writerLn(ans);

  return 0;
}


Fixed submission:
#define _CRT_SECURE_NO_WARNINGS

#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <functional>
#include <iostream>
#include <iterator>
#include <limits>
#include <map>
#include <memory>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;
#define FOR(i, n) for (int i = 0; i < (n); i++)
#define sz(c) ((int)c.size())
#define ten(n) ((int)1e##n)
using ll = long long;
using Pii = pair<int, int>;
using Pll = pair<ll, ll>;

template <typename...> static inline int getchar_unlocked(void) {
  return getchar();
}
template <typename...> static inline void putchar_unlocked(int c) {
  putchar(c);
}
#define mygc(c) (c) = getchar_unlocked()
#define mypc(c) putchar_unlocked(c)
void reader(int &x) {
  int k, m = 0;
  x = 0;
  for (;;) {
    mygc(k);
    if (k == '-') {
      m = 1;
      break;
    }
    if ('0' <= k && k <= '9') {
      x = k - '0';
      break;
    }
  }
  for (;;) {
    mygc(k);
    if (k < '0' || k > '9')
      break;
    x = x * 10 + k - '0';
  }
  if (m)
    x = -x;
}
void reader(ll &x) {
  int k, m = 0;
  x = 0;
  for (;;) {
    mygc(k);
    if (k == '-') {
      m = 1;
      break;
    }
    if ('0' <= k && k <= '9') {
      x = k - '0';
      break;
    }
  }
  for (;;) {
    mygc(k);
    if (k < '0' || k > '9')
      break;
    x = x * 10 + k - '0';
  }
  if (m)
    x = -x;
}
int reader(char c[]) {
  int i, s = 0;
  for (;;) {
    mygc(i);
    if (i != ' ' && i != '\n' && i != '\r' && i != '\t' && i != EOF)
      break;
  }
  c[s++] = i;
  for (;;) {
    mygc(i);
    if (i == ' ' || i == '\n' || i == '\r' || i == '\t' || i == EOF)
      break;
    c[s++] = i;
  }
  c[s] = '\0';
  return s;
}
int reader(string &c) {
  int i;
  for (;;) {
    mygc(i);
    if (i != ' ' && i != '\n' && i != '\r' && i != '\t' && i != EOF)
      break;
  }
  c.push_back(i);
  for (;;) {
    mygc(i);
    if (i == ' ' || i == '\n' || i == '\r' || i == '\t' || i == EOF)
      break;
    c.push_back(i);
  };
  return sz(c);
}
template <class T, class S> void reader(T &x, S &y) {
  reader(x);
  reader(y);
}
template <class T, class S, class U> void reader(T &x, S &y, U &z) {
  reader(x);
  reader(y);
  reader(z);
}
template <class T, class S, class U, class V>
void reader(T &x, S &y, U &z, V &w) {
  reader(x);
  reader(y);
  reader(z);
  reader(w);
}
void writer(int x, char c) {
  int s = 0, m = 0;
  char f[10];
  if (x < 0)
    m = 1, x = -x;
  while (x)
    f[s++] = x % 10, x /= 10;
  if (!s)
    f[s++] = 0;
  if (m)
    mypc('-');
  while (s--)
    mypc(f[s] + '0');
  mypc(c);
}
void writer(ll x, char c) {
  int s = 0, m = 0;
  char f[20];
  if (x < 0)
    m = 1, x = -x;
  while (x)
    f[s++] = x % 10, x /= 10;
  if (!s)
    f[s++] = 0;
  if (m)
    mypc('-');
  while (s--)
    mypc(f[s] + '0');
  mypc(c);
}
void writer(const char c[]) {
  int i;
  for (i = 0; c[i] != '\0'; i++)
    mypc(c[i]);
}
void writer(const string &x, char c) {
  int i;
  for (i = 0; x[i] != '\0'; i++)
    mypc(x[i]);
  mypc(c);
}
void writer(const char x[], char c) {
  int i;
  for (i = 0; x[i] != '\0'; i++)
    mypc(x[i]);
  mypc(c);
}
template <class T> void writerLn(T x) { writer(x, '\n'); }
template <class T, class S> void writerLn(T x, S y) {
  writer(x, ' ');
  writer(y, '\n');
}
template <class T, class S, class U> void writerLn(T x, S y, U z) {
  writer(x, ' ');
  writer(y, ' ');
  writer(z, '\n');
}
template <class T, class S, class U, class V>
void writerLn(T x, S y, U z, V v) {
  writer(x, ' ');
  writer(y, ' ');
  writer(z, ' ');
  writer(v, '\n');
}
template <class T> void writerArr(T x[], int n) {
  if (!n) {
    mypc('\n');
    return;
  }
  FOR(i, n - 1) writer(x[i], ' ');
  writer(x[n - 1], '\n');
}
template <class T> void writerArr(vector<T> &x) {
  writerArr(x.data(), (int)x.size());
}

template <class T> void chmin(T &a, const T &b) {
  if (a > b)
    a = b;
}
template <class T> void chmax(T &a, const T &b) {
  if (a < b)
    a = b;
}

template <class T> T gcd(T a, T b) { return b ? gcd(b, a % b) : a; }
template <class T> T lcm(T a, T b) { return a / gcd(a, b) * b; }
ll mod_pow(ll a, ll n, ll mod) {
  ll ret = 1;
  ll p = a % mod;
  while (n) {
    if (n & 1)
      ret = ret * p % mod;
    p = p * p % mod;
    n >>= 1;
  }
  return ret;
}
template <class T> T extgcd(T a, T b, T &x, T &y) {
  for (T u = y = 1, v = x = 0; a;) {
    T q = b / a;
    swap(x -= q * u, u);
    swap(y -= q * v, v);
    swap(b -= q * a, a);
  }
  return b;
}
ll mod_inv(ll a, ll m) {
  ll x, y;
  extgcd<ll>(a, m, x, y);
  return (m + x % m) % m;
}

#ifdef _DEBUG
template <typename... Args>
void debugPrintf(const char *format, Args const &...args) {
  fprintf(stdout, format, args...);
  fflush(stdout);
}
#else
#define debugPrintf(...)
#endif

ll a[3000];
ll memo[3001][3001][2];

ll dfs(int l, int r, bool f) {
  ll &ret = memo[l][r][f];
  if (ret != 0x8f8f8f8f8f8f8f8f)
    return ret;
  if (l == r)
    return ret = 0;

  if (f) {
    ll l1 = dfs(l + 1, r, !f) + a[l];
    ll l2 = dfs(l, r - 1, !f) + a[r - 1];
    return ret = max(l1, l2);
  } else {
    ll l1 = dfs(l + 1, r, !f) - a[l];
    ll l2 = dfs(l, r - 1, !f) - a[r - 1];
    return ret = min(l1, l2);
  }
}

int main() {
  int n;
  reader(n);
  FOR(i, n) reader(a[i]);
  memset(memo, 0x8f, sizeof(memo));
  ll ans = dfs(0, n, true);
  writerLn(ans);

  return 0;
}