Problem p03716 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>

#define _overload(_1, _2, _3, name, ...) name
#define _rep(i, n) _range(i, 0, n)
#define _range(i, a, b) for (int i = int(a); i < int(b); ++i)
#define rep(...) _overload(__VA_ARGS__, _range, _rep, )(__VA_ARGS__)

#define _rrep(i, n) _rrange(i, n, 0)
#define _rrange(i, a, b) for (int i = int(a) - 1; i >= int(b); --i)
#define rrep(...) _overload(__VA_ARGS__, _rrange, _rrep, )(__VA_ARGS__)

#define _all(arg) begin(arg), end(arg)
#define uniq(arg) sort(_all(arg)), (arg).erase(unique(_all(arg)), end(arg))
#define getidx(ary, key) lower_bound(_all(ary), key) - begin(ary)
#define clr(a, b) memset((a), (b), sizeof(a))
#define bit(n) (1LL << (n))
#define popcount(n) (__builtin_popcountll(n))

using namespace std;

template <class T> bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T> bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}

typedef long long ll;
typedef long double R;
const R EPS = 1e-9L; // [-1000,1000]->EPS=1e-8 [-10000,10000]->EPS=1e-7
inline int sgn(const R &r) { return (r > EPS) - (r < -EPS); }
inline R sq(R x) { return sqrt(max(x, 0.0L)); }

const int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};

// Problem Specific Parameter:

int main() {
  long long N;
  cin >> N;
  vector<long long> a(3 * N);
  vector<long long> s(3 * N), t(3 * N);
  long long cnt, cnt2;
  priority_queue<long long, vector<long long>, greater<long long>> L;
  priority_queue<long long, vector<long long>, less<long long>> R;
  for (int i = 0; i < 3 * N; ++i) {
    cin >> a[i];
  }
  for (int i = 0; i < N; ++i) {
    L.emplace(a[i]);
    cnt += a[i];
  }
  s[N] = cnt;
  for (int i = N; i < 3 * N; ++i) {
    L.emplace(a[i]);
    cnt += a[i];
    cnt2 += a[i];
    cnt -= L.top();
    L.pop();
    s[i + 1] = cnt;
  }
  cnt = 0, cnt2 = 0;
  for (int i = 2 * N; i < 3 * N; ++i) {
    R.emplace(a[i]);
    cnt += a[i];
    cnt2 += a[i];
  }
  t[2 * N] = cnt;
  for (int i = 2 * N - 1; i >= 0; --i) {
    R.emplace(a[i]);
    cnt += a[i];
    cnt -= R.top();
    R.pop();
    t[i] = cnt;
  }
  long long maxn = (-1LL << 60);
  for (int i = N; i <= 2 * N; ++i) {
    maxn = max(maxn, s[i] - t[i]);
  }
  cout << maxn << endl;

  return 0;
}


Fixed submission:
#include <bits/stdc++.h>

#define _overload(_1, _2, _3, name, ...) name
#define _rep(i, n) _range(i, 0, n)
#define _range(i, a, b) for (int i = int(a); i < int(b); ++i)
#define rep(...) _overload(__VA_ARGS__, _range, _rep, )(__VA_ARGS__)

#define _rrep(i, n) _rrange(i, n, 0)
#define _rrange(i, a, b) for (int i = int(a) - 1; i >= int(b); --i)
#define rrep(...) _overload(__VA_ARGS__, _rrange, _rrep, )(__VA_ARGS__)

#define _all(arg) begin(arg), end(arg)
#define uniq(arg) sort(_all(arg)), (arg).erase(unique(_all(arg)), end(arg))
#define getidx(ary, key) lower_bound(_all(ary), key) - begin(ary)
#define clr(a, b) memset((a), (b), sizeof(a))
#define bit(n) (1LL << (n))
#define popcount(n) (__builtin_popcountll(n))

using namespace std;

template <class T> bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T> bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}

typedef long long ll;
typedef long double R;
const R EPS = 1e-9L; // [-1000,1000]->EPS=1e-8 [-10000,10000]->EPS=1e-7
inline int sgn(const R &r) { return (r > EPS) - (r < -EPS); }
inline R sq(R x) { return sqrt(max(x, 0.0L)); }

const int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};

// Problem Specific Parameter:

int main() {
  long long N;
  cin >> N;
  vector<long long> a(400000);
  vector<long long> s(400000), t(400000);
  long long cnt, cnt2;
  priority_queue<long long, vector<long long>, greater<long long>> L;
  priority_queue<long long, vector<long long>, less<long long>> R;
  for (int i = 0; i < 3 * N; ++i) {
    cin >> a[i];
  }
  for (int i = 0; i < N; ++i) {
    L.emplace(a[i]);
    cnt += a[i];
  }
  s[N] = cnt;
  for (int i = N; i < 3 * N; ++i) {
    L.emplace(a[i]);
    cnt += a[i];
    cnt2 += a[i];
    cnt -= L.top();
    L.pop();
    s[i + 1] = cnt;
  }
  cnt = 0, cnt2 = 0;
  for (int i = 2 * N; i < 3 * N; ++i) {
    R.emplace(a[i]);
    cnt += a[i];
    cnt2 += a[i];
  }
  t[2 * N] = cnt;
  for (int i = 2 * N - 1; i >= 0; --i) {
    R.emplace(a[i]);
    cnt += a[i];
    cnt -= R.top();
    R.pop();
    t[i] = cnt;
  }
  long long maxn = (-1LL << 60);
  for (int i = N; i <= 2 * N; ++i) {
    maxn = max(maxn, s[i] - t[i]);
  }
  cout << maxn << endl;

  return 0;
}