Problem p02716 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/detail/standard_policies.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define ll long long
#define int long long
#define pb push_back
#define ins insert
#define rs resize
#define br break;
#define cont continue;
#define vi vector<int>
#define vll vector<long long>
#define vvi vector<vector<int>>
#define si set<ll>
#define sll set<long long>
#define pii pair<ll, ll>
#define pll pair<long long, long long>
#define speed                                                                  \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(NULL);
#define vec vector
#define cend cout << endl;
#define sc second
#define fr first
#define retz return 0;
#define ll_MAX (ll)(1e9 * 1e9)
#define ll_MIN (ll)(-1e9 * 1e9)
#define lb lower_bound
#define ub upper_bound
#define rep(i, a, b) for (int i = a; i <= b; i++)
#define repd(i, a, b) for (int i = a; i >= b; i--)
#define ps(arr, n)                                                             \
  for (int i = 1; i < n; i++)                                                  \
    arr[i] += arr[i - 1];
#define inp(arr, n)                                                            \
  for (int i = 0; i < n; i++)                                                  \
    cin >> arr[i];
#define out(arr, n)                                                            \
  for (int i = 0; i < n; i++)                                                  \
    cout << arr[i];
#define inp1(arr, n, m)                                                        \
  for (int i = 0; i < n; i++)                                                  \
    for (int j = 0; j < m; j++)                                                \
      cin >> arr[i][j];
#define out1(arr, n, m)                                                        \
  for (int i = 0; i < n; i++)                                                  \
    for (int j = 0; j < m; j++)                                                \
      cin >> arr[i][j];
#define loop(q) for (auto it : q)
#define loop1(q) for (auto &it : q)
#define db1 cout << "*" << endl
#define db2 cout << "YES" << endl
using namespace std;
using namespace __gnu_pbds;
#define oset(X)                                                                \
  tree<X, null_type, less<X>, rb_tree_tag, tree_order_statistics_node_update>
#define roset(X)                                                               \
  tree<X, null_type, greater<X>, rb_tree_tag, tree_order_statistics_node_update>
#define okey order_of_key // lower_bound_set
#define ofind find_by_order
#define cyes cout << "Yes" << endl;
#define cno cout << "No" << endl;
#define mod (long long)1000000007
#define mod2 (long long)998244353
#define INT_MAX1 900000000
#define MAXN 2000000
#define INF INT_MAX

int dp[1000001][5];
bool v[1000001][5];
int n;
int arr[1000001];

int s1(int i, int d) {
  if (d < 0)
    return -1e15;
  if (i >= n)
    return 0;
  if (v[i][d])
    return dp[i][d];
  return dp[i][d] = max((arr[i] + s1(i + 2, d)), s1(i + 1, d - 1));
}

void solve() {
  cin >> n;
  inp(arr, n);
  if (n % 2 == 0)
    cout << s1(0, 1) << endl;
  else
    cout << s1(0, 2) << endl;
}

signed main() {

  speed;
  int t = 1;
  // cin >> t;
  while (t--)
    solve();
}

Fixed submission:
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/detail/standard_policies.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define ll long long
#define int long long
#define pb push_back
#define ins insert
#define rs resize
#define br break;
#define cont continue;
#define vi vector<int>
#define vll vector<long long>
#define vvi vector<vector<int>>
#define si set<ll>
#define sll set<long long>
#define pii pair<ll, ll>
#define pll pair<long long, long long>
#define speed                                                                  \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(NULL);
#define vec vector
#define cend cout << endl;
#define sc second
#define fr first
#define retz return 0;
#define ll_MAX (ll)(1e9 * 1e9)
#define ll_MIN (ll)(-1e9 * 1e9)
#define lb lower_bound
#define ub upper_bound
#define rep(i, a, b) for (int i = a; i <= b; i++)
#define repd(i, a, b) for (int i = a; i >= b; i--)
#define ps(arr, n)                                                             \
  for (int i = 1; i < n; i++)                                                  \
    arr[i] += arr[i - 1];
#define inp(arr, n)                                                            \
  for (int i = 0; i < n; i++)                                                  \
    cin >> arr[i];
#define out(arr, n)                                                            \
  for (int i = 0; i < n; i++)                                                  \
    cout << arr[i];
#define inp1(arr, n, m)                                                        \
  for (int i = 0; i < n; i++)                                                  \
    for (int j = 0; j < m; j++)                                                \
      cin >> arr[i][j];
#define out1(arr, n, m)                                                        \
  for (int i = 0; i < n; i++)                                                  \
    for (int j = 0; j < m; j++)                                                \
      cin >> arr[i][j];
#define loop(q) for (auto it : q)
#define loop1(q) for (auto &it : q)
#define db1 cout << "*" << endl
#define db2 cout << "YES" << endl
using namespace std;
using namespace __gnu_pbds;
#define oset(X)                                                                \
  tree<X, null_type, less<X>, rb_tree_tag, tree_order_statistics_node_update>
#define roset(X)                                                               \
  tree<X, null_type, greater<X>, rb_tree_tag, tree_order_statistics_node_update>
#define okey order_of_key // lower_bound_set
#define ofind find_by_order
#define cyes cout << "Yes" << endl;
#define cno cout << "No" << endl;
#define mod (long long)1000000007
#define mod2 (long long)998244353
#define INT_MAX1 900000000
#define MAXN 2000000
#define INF INT_MAX

int dp[1000001][5];
bool v[1000001][5];
int n;
int arr[1000001];

int s1(int i, int d) {
  if (d < 0)
    return -1e15;
  if (i >= n)
    return 0;
  if (v[i][d])
    return dp[i][d];
  v[i][d] = 1;
  return dp[i][d] = max((arr[i] + s1(i + 2, d)), s1(i + 1, d - 1));
}

void solve() {
  cin >> n;
  inp(arr, n);
  if (n % 2 == 0)
    cout << s1(0, 1) << endl;
  else
    cout << s1(0, 2) << endl;
}

signed main() {

  speed;
  int t = 1;
  // cin >> t;
  while (t--)
    solve();
}