Problem p02913 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using vl = vector<ll>;
template <class T> using vc = vector<T>;
template <class T> using vvc = vector<vector<T>>;

#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define rep(i, n) for (ll i = 0; i < (n); i++)
#define repr(i, n) for (ll i = (n)-1; i >= 0; i--)
#define repe(i, l, r) for (ll i = (l); i < (r); i++)
#define reper(i, l, r) for (ll i = (r)-1; i >= (l); i--)
#define repa(i, n) for (auto &i : n)

template <class T> inline bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
struct init {
  init() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(15);
  }
} init_;

#ifdef DEBUG
template <class T, class N> void verr(const T &a, const N &n) {
  rep(i, n) cerr << a[i] << " ";
  cerr << "\n" << flush;
}
ll dbgt = 1;
void err() { cerr << "passed " << dbgt++ << "\n" << flush; }
template <class H, class... T> void err(H &&h, T &&...t) {
  cerr << h << (sizeof...(t) ? " " : "\n") << flush;
  if (sizeof...(t) > 0)
    err(forward<T>(t)...);
}
#endif

const ll INF = 4e18;
const ld EPS = 1e-11;
const ld PI = acos(-1.0L);
const ll MOD = 1e9 + 7;
// const ll MOD = 998244353;
//--------------------------------------------------------------------------------//

int main() {
  ll N;
  cin >> N;
  string S;
  cin >> S;

  ll ans = 0;
  repe(n, 1, N) {
    string s = S.substr(0, n), t = S.substr(n, N - n);
    ll sn = n, tn = N - n;

    vvc<ll> dp(sn + 1, vl(tn + 1));
    rep(i, sn) rep(j, tn) {
      if (s[i] == t[j])
        chmax(dp[i + 1][j + 1], dp[i][j] + 1), chmax(ans, dp[i + 1][j + 1]);
    }
  }

  cout << ans << endl;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using vl = vector<ll>;
template <class T> using vc = vector<T>;
template <class T> using vvc = vector<vector<T>>;

#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define rep(i, n) for (ll i = 0; i < (n); i++)
#define repr(i, n) for (ll i = (n)-1; i >= 0; i--)
#define repe(i, l, r) for (ll i = (l); i < (r); i++)
#define reper(i, l, r) for (ll i = (r)-1; i >= (l); i--)
#define repa(i, n) for (auto &i : n)

template <class T> inline bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
struct init {
  init() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(15);
  }
} init_;

#ifdef DEBUG
template <class T, class N> void verr(const T &a, const N &n) {
  rep(i, n) cerr << a[i] << " ";
  cerr << "\n" << flush;
}
ll dbgt = 1;
void err() { cerr << "passed " << dbgt++ << "\n" << flush; }
template <class H, class... T> void err(H &&h, T &&...t) {
  cerr << h << (sizeof...(t) ? " " : "\n") << flush;
  if (sizeof...(t) > 0)
    err(forward<T>(t)...);
}
#endif

const ll INF = 4e18;
const ld EPS = 1e-11;
const ld PI = acos(-1.0L);
const ll MOD = 1e9 + 7;
// const ll MOD = 998244353;
//--------------------------------------------------------------------------------//

int main() {
  ll N;
  cin >> N;
  string S;
  cin >> S;

  ll ans = 0;
  vvc<ll> dp(N + 1, vl(N + 1));
  rep(i, N) repe(j, i + 1, N) {
    if (S[i] == S[j]) {
      chmax(dp[i + 1][j + 1], dp[i][j] + 1);
      chmax(ans, min(j - i, dp[i + 1][j + 1]));
    }
  }

  cout << ans << endl;
}