Problem p03309 (C++)

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

#define ll long long
#define db long double
#define ii pair<int, int>
#define vi vector<int>
#define fi first
#define se second
#define sz(a) (int)(a).size()
#define all(a) (a).begin(), (a).end()
#define pb push_back
#define mp make_pair
#define FN(i, n) for (int i = 0; i < (int)(n); ++i)
#define FEN(i, n) for (int i = 1; i <= (int)(n); ++i)
#define rep(i, a, b) for (int i = a; i < b; i++)
#define repv(i, a, b) for (int i = b - 1; i >= a; i--)
#define SET(A, val) memset(A, val, sizeof(A))
typedef tree<int, null_type, less<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    ordered_set;
// order_of_key (val): returns the no. of values less than val
// find_by_order (k): returns the kth largest element.(0-based)
#define TRACE
#ifdef TRACE
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  cerr << name << " : " << arg1 << std::endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
#else
#define trace(...)
#endif
const int N = 100005;
int a[N];
ll pre[N];
int main() {
  std::ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int n;
  cin >> n;
  rep(i, 1, n + 1) cin >> a[i];
  vi v;
  rep(i, 1, n + 1) v.pb(a[i] - i);
  sort(all(v));
  pre[0] = v[0];
  rep(i, 1, sz(v)) pre[i] = pre[i - 1] + v[i];
  ll ans = LLONG_MAX;
  rep(i, 0, sz(v)) ans = min(ans, (ll)(i + 1) * v[i] - pre[i] + pre[n - 1] -
                                      pre[i] - (ll)(n - 1 - i) * v[i]);
  cout << ans << endl;
  return 0;
}


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

#define ll long long
#define db long double
#define ii pair<int, int>
#define vi vector<int>
#define fi first
#define se second
#define sz(a) (int)(a).size()
#define all(a) (a).begin(), (a).end()
#define pb push_back
#define mp make_pair
#define FN(i, n) for (int i = 0; i < (int)(n); ++i)
#define FEN(i, n) for (int i = 1; i <= (int)(n); ++i)
#define rep(i, a, b) for (int i = a; i < b; i++)
#define repv(i, a, b) for (int i = b - 1; i >= a; i--)
#define SET(A, val) memset(A, val, sizeof(A))
typedef tree<int, null_type, less<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    ordered_set;
// order_of_key (val): returns the no. of values less than val
// find_by_order (k): returns the kth largest element.(0-based)
#define TRACE
#ifdef TRACE
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  cerr << name << " : " << arg1 << std::endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
#else
#define trace(...)
#endif
const int N = 200005;
int a[N];
ll pre[N];
int main() {
  std::ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int n;
  cin >> n;
  rep(i, 1, n + 1) cin >> a[i];
  vi v;
  rep(i, 1, n + 1) v.pb(a[i] - i);
  sort(all(v));
  pre[0] = v[0];
  rep(i, 1, sz(v)) pre[i] = pre[i - 1] + v[i];
  ll ans = LLONG_MAX;
  rep(i, 0, sz(v)) ans = min(ans, (ll)(i + 1) * v[i] - pre[i] + pre[n - 1] -
                                      pre[i] - (ll)(n - 1 - i) * v[i]);
  cout << ans << endl;
  return 0;
}