Problem p03160 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
using namespace std;

#define ff first
#define ss second
#define int long long int
#define pb push_back
#define mp make_pair
#define pii pair<int, int>
#define vi vector<int>
#define mii map<int, int>
#define pqb priority_queue<int>
#define pqs priority_queue<int, vi, greater<int>>
#define setbits(x) __builtin_popcountll(x)
#define zrobits(x) __builtin_ctzll(x)
#define mod 1000000007
#define inf 1e18
#define ps(x, y) fixed << setprecision(y) << x
#define mk(arr, n, type) type *arr = new type[n];
#define w(x)                                                                   \
  int x;                                                                       \
  cin >> x;                                                                    \
  while (x--)
#define from(i, n) for (int i = 0; i < (int)n; i++)
#define from_j(i, j, n) for (int i = j; i < (int)n; i++)
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

typedef tree<int, null_type, less<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    pbds;

void c_p_c() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif
}

int32_t main() {
  c_p_c();
  int n;
  cin >> n;
  int arr[n];
  from(i, n) cin >> arr[i];
  int cost[n];
  cost[0] = 0;
  cost[1] = abs(arr[1] - arr[0]);
  for (int i = 2; i < n; i++) {
    cost[i] = min(cost[i - 1] + abs(arr[i] - arr[i - 1]),
                  cost[i - 2] + abs(arr[i] - arr[i - 2]));
  }
  cout << cost[n - 1];
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
using namespace std;

#define ff first
#define ss second
#define int long long int
#define pb push_back
#define mp make_pair
#define pii pair<int, int>
#define vi vector<int>
#define mii map<int, int>
#define pqb priority_queue<int>
#define pqs priority_queue<int, vi, greater<int>>
#define setbits(x) __builtin_popcountll(x)
#define zrobits(x) __builtin_ctzll(x)
#define mod 1000000007
#define inf 1e18
#define ps(x, y) fixed << setprecision(y) << x
#define mk(arr, n, type) type *arr = new type[n];
#define w(x)                                                                   \
  int x;                                                                       \
  cin >> x;                                                                    \
  while (x--)
#define from(i, n) for (int i = 0; i < (int)n; i++)
#define from_j(i, j, n) for (int i = j; i < (int)n; i++)
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

typedef tree<int, null_type, less<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    pbds;

void c_p_c() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
}

int32_t main() {
  c_p_c();
  int n;
  cin >> n;
  int arr[n];
  from(i, n) cin >> arr[i];
  int cost[n];
  cost[0] = 0;
  cost[1] = abs(arr[1] - arr[0]);
  for (int i = 2; i < n; i++) {
    cost[i] = min(cost[i - 1] + abs(arr[i] - arr[i - 1]),
                  cost[i - 2] + abs(arr[i] - arr[i - 2]));
  }
  cout << cost[n - 1];
  return 0;
}