Problem p03309 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <bitset>
#include <climits>
#include <cmath>
#include <complex>
#include <ctime>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <vector>

using namespace std;

#define IOS                                                                    \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(0)
#define all(x) x.begin(), x.end()
#define ff first
#define ss second
#define MOD 1000000007LL
#define rep(i, a, n) for (int i = a; i < n; i++)
#define per(i, a, n) for (int i = n - 1; i >= a; i--)
#define LLINF 100000000000000005LL
#define INF (int)1e9 + 1
#define endl '\n'
#define pb push_back

// debug 도구

template <typename A, typename B> string to_string(pair<A, B> p);

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);

string to_string(const string &s) { return '"' + s + '"'; }

string to_string(const char *s) { return to_string((string)s); }

string to_string(bool b) { return (b ? "true" : "false"); }

string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}

template <size_t N> string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}

template <typename A> string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}\n";
  return res;
}

template <typename A, typename B> string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ")";
}

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:\n", debug_out(__VA_ARGS__)

// debug 도구 end

using llong = long long;
using VI = vector<int>;
using VVI = vector<vector<int>>;
using VPII = vector<pair<int, int>>;
using VLL = vector<long long>;
using PII = pair<int, int>;

int main() {
  int n;
  cin >> n;
  VLL a(n);
  rep(i, 0, n) {
    cin >> a[i];
    a[i] -= i + 1;
  }
  llong mmin = LLINF;
  rep(i, 0, n) {
    llong sum = 0;
    rep(j, 0, n) { sum += abs(a[i] - a[j]); }
    mmin = min(mmin, sum);
  }
  cout << mmin;
  return 0;
}

Fixed submission:
#include <algorithm>
#include <bitset>
#include <climits>
#include <cmath>
#include <complex>
#include <ctime>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <vector>

using namespace std;

#define IOS                                                                    \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(0)
#define all(x) x.begin(), x.end()
#define ff first
#define ss second
#define MOD 1000000007LL
#define rep(i, a, n) for (int i = a; i < n; i++)
#define per(i, a, n) for (int i = n - 1; i >= a; i--)
#define LLINF 100000000000000005LL
#define INF (int)1e9 + 1
#define endl '\n'
#define pb push_back

// debug 도구

template <typename A, typename B> string to_string(pair<A, B> p);

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);

string to_string(const string &s) { return '"' + s + '"'; }

string to_string(const char *s) { return to_string((string)s); }

string to_string(bool b) { return (b ? "true" : "false"); }

string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}

template <size_t N> string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}

template <typename A> string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}\n";
  return res;
}

template <typename A, typename B> string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ")";
}

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:\n", debug_out(__VA_ARGS__)

// debug 도구 end

using llong = long long;
using VI = vector<int>;
using VVI = vector<vector<int>>;
using VPII = vector<pair<int, int>>;
using VLL = vector<long long>;
using PII = pair<int, int>;

int main() {
  int n;
  cin >> n;
  VLL a(n);
  rep(i, 0, n) {
    cin >> a[i];
    a[i] -= i + 1;
  }
  sort(all(a));
  llong ans = a[a.size() / 2];
  llong sum = 0;
  rep(i, 0, n) { sum += abs(ans - a[i]); }
  cout << sum;
  return 0;
}