Problem p03180 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
#define repr(i, a, b) for (int i = a; i < b; i++)
#define rep(i, n) for (int i = 0; i < n; i++)
#define reprrev(i, a, b) for (int i = b - 1; i >= a; i--) // [a, b)
#define reprev(i, n) reprrev(i, 0, n)
typedef long long ll;
typedef unsigned long long ull;
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

/* attention
    long longのシフト演算には気をつけよう
    タイポした時のデバッグが死ぬほどきつくなるので変数名は最低3字くらい使った方がいいかも
    sizeは(int)とキャストしよう
    cin.tie(0);
    ios::sync_with_stdio(false);<- これら、printfとかと併用しない方が良さそう

*/

const ll mod = 1e9 + 7;

void chmod(ll &M) {
  if (M >= mod)
    M %= mod;
  else if (M < 0) {
    M += (abs(M) / mod + 1) * mod;
    M %= mod;
  }
}

ll modpow(ll x, ll n) {
  if (n == 0)
    return 1;
  ll res = modpow(x, n / 2);

  if (n % 2 == 0)
    return res * res % mod;
  else
    return res * res % mod * x % mod;
}

int getl(int i, int N) { return i == 0 ? N - 1 : i - 1; };
int getr(int i, int N) { return i == N - 1 ? 0 : i + 1; };

// 線分 ab の偏角 返り値は[-π, π]
double argument(const pair<double, double> &a, const pair<double, double> &b) {
  double ax = a.first, ay = a.second, bx = b.first, by = b.second;
  return atan2(by - ay, bx - ax);
}

/* <----------------------------------------------------------------------------------->
 */
/* <----------------------------------------------------------------------------------->
 */
/* <----------------------------------------------------------------------------------->
 */
/* <----------------------------------------------------------------------------------->
 */

int N;
vector<vector<ll>> a;
vector<ll> memo(1 << 18, 0);
vector<bool> flg(1 << 18, false);

ll rec(int S) {
  if (flg[S])
    return memo[S];

  ll tmp = 0;
  rep(i, N) repr(j, i + 1, N) if (S & 1 << i && S & 1 << j) tmp += a[i][j];

  for (int T = S - 1; T > 0; T = (T - 1) & S) {
    chmax(tmp, rec(T) + rec(S ^ T));
  }

  flg[S] = true;
  return memo[S] = tmp;
}

int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);

  cin >> N;
  a.resize(N, vector<ll>(N, 0));
  rep(i, N) rep(j, N) cin >> a[i][j];

  cout << rec((1 << N) - 1) << endl;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#define repr(i, a, b) for (int i = a; i < b; i++)
#define rep(i, n) for (int i = 0; i < n; i++)
#define reprrev(i, a, b) for (int i = b - 1; i >= a; i--) // [a, b)
#define reprev(i, n) reprrev(i, 0, n)
typedef long long ll;
typedef unsigned long long ull;
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

/* attention
    long longのシフト演算には気をつけよう
    タイポした時のデバッグが死ぬほどきつくなるので変数名は最低3字くらい使った方がいいかも
    sizeは(int)とキャストしよう
    cin.tie(0);
    ios::sync_with_stdio(false);<- これら、printfとかと併用しない方が良さそう

*/

const ll mod = 1e9 + 7;

void chmod(ll &M) {
  if (M >= mod)
    M %= mod;
  else if (M < 0) {
    M += (abs(M) / mod + 1) * mod;
    M %= mod;
  }
}

ll modpow(ll x, ll n) {
  if (n == 0)
    return 1;
  ll res = modpow(x, n / 2);

  if (n % 2 == 0)
    return res * res % mod;
  else
    return res * res % mod * x % mod;
}

int getl(int i, int N) { return i == 0 ? N - 1 : i - 1; };
int getr(int i, int N) { return i == N - 1 ? 0 : i + 1; };

// 線分 ab の偏角 返り値は[-π, π]
double argument(const pair<double, double> &a, const pair<double, double> &b) {
  double ax = a.first, ay = a.second, bx = b.first, by = b.second;
  return atan2(by - ay, bx - ax);
}

/* <----------------------------------------------------------------------------------->
 */
/* <----------------------------------------------------------------------------------->
 */
/* <----------------------------------------------------------------------------------->
 */
/* <----------------------------------------------------------------------------------->
 */

int N;
vector<vector<ll>> a;
vector<ll> memo(1 << 18, 0);
vector<bool> flg(1 << 18, false);

ll rec(int S) {
  if (flg[S])
    return memo[S];

  ll tmp = 0;
  rep(i, N) repr(j, i + 1, N) if (S & 1 << i && S & 1 << j) tmp += a[i][j];

  for (int T = (S - 1) & S; T > 0; T = (T - 1) & S) {
    chmax(tmp, rec(T) + rec(S ^ T));
  }

  flg[S] = true;
  return memo[S] = tmp;
}

int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);

  cin >> N;
  a.resize(N, vector<ll>(N, 0));
  rep(i, N) rep(j, N) cin >> a[i][j];

  cout << rec((1 << N) - 1) << endl;
}