Problem p04047 (C++)

Buggy submission (status: Runtime Error):
const int LG = 21;
const int FN = 400005;
const long long MOD = 998244353;
const long long INF = 1e9;
const long long INFLL = 1e18;

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;

#define forn(i, n) for (int(i) = 0; (i) != (n); (i)++)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define popcount(x) __builtin_popcount(x)
#define popcountll(x) __builtin_popcountll(x)
#define fi first
#define se second
#define re return
#define pb push_back
#define uniq(x)                                                                \
  sort(all(x));                                                                \
  (x).resize(unique(all(x)) - (x).begin())

#ifdef LOCAL
#define dbg(x) cerr << __LINE__ << " " << #x << " " << x << endl
#define ln cerr << __LINE__ << endl
#else
#define dbg(x) void(0)
#define ln void(0)
#endif // LOCAL

int cx[4] = {-1, 0, 1, 0};
int cy[4] = {0, -1, 0, 1};

ll inq(ll x, ll y) {
  if (!y)
    re 1 % MOD;
  ll l = inq(x, y / 2);
  if (y % 2)
    re l *l % MOD *x % MOD;
  re l *l % MOD;
}

ll rev(ll x) { return inq(x, MOD - 2); }

bool __precomputed_combinatorics = 0;
vector<ll> __fact, __ufact, __rev;

void __precompute_combinatorics() {
  __precomputed_combinatorics = 1;
  __fact.resize(FN);
  __ufact.resize(FN);
  __rev.resize(FN);
  __rev[1] = 1;
  for (int i = 2; i < FN; i++)
    __rev[i] = MOD - __rev[MOD % i] * (MOD / i) % MOD;
  __fact[0] = 1, __ufact[0] = 1;
  for (int i = 1; i < FN; i++)
    __fact[i] = __fact[i - 1] * i % MOD,
    __ufact[i] = __ufact[i - 1] * __rev[i] % MOD;
}

ll fact(int x) {
  if (!__precomputed_combinatorics)
    __precompute_combinatorics();
  return __fact[x];
}

ll cnk(int n, int k) {
  if (k < 0 || k > n)
    return 0;
  if (!__precomputed_combinatorics)
    __precompute_combinatorics();
  return __fact[n] * __ufact[n - k] % MOD * __ufact[k] % MOD;
}

int Root(int x, vector<int> &root) {
  if (x == root[x])
    return x;
  return root[x] = Root(root[x], root);
}

void Merge(int v, int u, vector<int> &root, vector<int> &sz) {
  v = Root(v, root), u = Root(u, root);
  if (v == u)
    return;
  if (sz[v] < sz[u]) {
    sz[u] += sz[v];
    root[v] = u;
  } else {
    sz[v] += sz[u];
    root[u] = v;
  }
}

int ok(int x, int n) { return 0 <= x && x < n; }

const int N = 1100000;

signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  ll n, m, k;
  cin >> n;
  vi a(n);
  forn(i, 2 * n) cin >> a[i];
  sort(all(a));
  ll ans = 0;
  forn(i, n) ans += min(a[2 * i], a[2 * i + 1]);
  cout << ans;
}

/* Note:
Check constants at the beginning of the code.
    N is set to 4e5 but be careful in problems with large constant factor.
    Setting N in every problem is more effective.
Check corner cases.
    N = 1
No def int long long for now.
Add something here.
*/


Fixed submission:
const int LG = 21;
const int FN = 400005;
const long long MOD = 998244353;
const long long INF = 1e9;
const long long INFLL = 1e18;

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;

#define forn(i, n) for (int(i) = 0; (i) != (n); (i)++)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define popcount(x) __builtin_popcount(x)
#define popcountll(x) __builtin_popcountll(x)
#define fi first
#define se second
#define re return
#define pb push_back
#define uniq(x)                                                                \
  sort(all(x));                                                                \
  (x).resize(unique(all(x)) - (x).begin())

#ifdef LOCAL
#define dbg(x) cerr << __LINE__ << " " << #x << " " << x << endl
#define ln cerr << __LINE__ << endl
#else
#define dbg(x) void(0)
#define ln void(0)
#endif // LOCAL

int cx[4] = {-1, 0, 1, 0};
int cy[4] = {0, -1, 0, 1};

ll inq(ll x, ll y) {
  if (!y)
    re 1 % MOD;
  ll l = inq(x, y / 2);
  if (y % 2)
    re l *l % MOD *x % MOD;
  re l *l % MOD;
}

ll rev(ll x) { return inq(x, MOD - 2); }

bool __precomputed_combinatorics = 0;
vector<ll> __fact, __ufact, __rev;

void __precompute_combinatorics() {
  __precomputed_combinatorics = 1;
  __fact.resize(FN);
  __ufact.resize(FN);
  __rev.resize(FN);
  __rev[1] = 1;
  for (int i = 2; i < FN; i++)
    __rev[i] = MOD - __rev[MOD % i] * (MOD / i) % MOD;
  __fact[0] = 1, __ufact[0] = 1;
  for (int i = 1; i < FN; i++)
    __fact[i] = __fact[i - 1] * i % MOD,
    __ufact[i] = __ufact[i - 1] * __rev[i] % MOD;
}

ll fact(int x) {
  if (!__precomputed_combinatorics)
    __precompute_combinatorics();
  return __fact[x];
}

ll cnk(int n, int k) {
  if (k < 0 || k > n)
    return 0;
  if (!__precomputed_combinatorics)
    __precompute_combinatorics();
  return __fact[n] * __ufact[n - k] % MOD * __ufact[k] % MOD;
}

int Root(int x, vector<int> &root) {
  if (x == root[x])
    return x;
  return root[x] = Root(root[x], root);
}

void Merge(int v, int u, vector<int> &root, vector<int> &sz) {
  v = Root(v, root), u = Root(u, root);
  if (v == u)
    return;
  if (sz[v] < sz[u]) {
    sz[u] += sz[v];
    root[v] = u;
  } else {
    sz[v] += sz[u];
    root[u] = v;
  }
}

int ok(int x, int n) { return 0 <= x && x < n; }

const int N = 1100000;

signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  ll n, m, k;
  cin >> n;
  vi a(2 * n);
  forn(i, 2 * n) cin >> a[i];
  sort(all(a));
  ll ans = 0;
  forn(i, n) ans += min(a[2 * i], a[2 * i + 1]);
  cout << ans;
}

/* Note:
Check constants at the beginning of the code.
    N is set to 4e5 but be careful in problems with large constant factor.
    Setting N in every problem is more effective.
Check corner cases.
    N = 1
No def int long long for now.
Add something here.
*/