Problem p02913 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;

// Define
using ll = long long;
using ull = unsigned long long;
using ld = long double;
template <class T> using pvector = vector<pair<T, T>>;
template <class T>
using rpriority_queue = priority_queue<T, vector<T>, greater<T>>;
constexpr const ll dx[4] = {1, 0, -1, 0};
constexpr const ll dy[4] = {0, 1, 0, -1};
constexpr const ll MOD = 1e9 + 7;
constexpr const ll mod = 998244353;
constexpr const ll INF = 1LL << 60;
constexpr const ll inf = 1 << 30;
constexpr const char rt = '\n';
constexpr const char sp = ' ';
#define rt(i, n) (i == (ll)(n)-1 ? rt : sp)
#define len(x) ((ll)(x).size())
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define eb emplace_back
#define ifn(x) if (not(x))
#define elif else if
#define elifn else ifn
#define fi first
#define se second

using graph = vector<vector<ll>>;
template <class T> using wgraph = vector<vector<ll, T>>;
bool __DIRECTED__ = true;
istream &operator>>(istream &is, graph &g) {
  ll a, b;
  is >> a >> b;
  g[a - 1].pb(b - 1);
  if (__DIRECTED__ == false)
    g[b - 1].pb(a - 1);
  return is;
}

template <class T> istream &operator>>(istream &is, wgraph<T> &g) {
  ll a, b;
  T c;
  is >> a >> b >> c;
  g[a - 1].pb({b - 1, c});
  if (__DIRECTED__ == false)
    g[b - 1].pb({a - 1, c});
  return is;
}

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

// Debug
#define debug(...)                                                             \
  {                                                                            \
    cerr << __LINE__ << ": " << #__VA_ARGS__ << " = ";                         \
    for (auto &&X : {__VA_ARGS__})                                             \
      cerr << "[" << X << "] ";                                                \
    cerr << rt;                                                                \
  }

#define dump(a, h, w)                                                          \
  {                                                                            \
    cerr << __LINE__ << ": " << #a << " = [" << rt;                            \
    rep(_i, h) {                                                               \
      rep(_j, w) {                                                             \
        if (abs(a[_i][_j]) >= INF / 2 and a[_i][_j] <= -INF / 2)               \
          cerr << '-';                                                         \
        if (abs(a[_i][_j]) >= INF / 2)                                         \
          cerr << "∞" << sp;                                                   \
        else                                                                   \
          cerr << a[_i][_j] << sp;                                             \
      }                                                                        \
      cerr << rt;                                                              \
    }                                                                          \
    cerr << "]" << rt;                                                         \
  }

#define vdump(a, n)                                                            \
  {                                                                            \
    cerr << __LINE__ << ": " << #a << " = [";                                  \
    rep(_i, n) {                                                               \
      if (_i)                                                                  \
        cerr << sp;                                                            \
      if (abs(a[_i]) >= INF / 2 and a[_i] <= -INF / 2)                         \
        cerr << '-';                                                           \
      if (abs(a[_i]) >= INF / 2)                                               \
        cerr << "∞" << sp;                                                     \
      else                                                                     \
        cerr << a[_i];                                                         \
    }                                                                          \
    cerr << "]" << rt;                                                         \
  }

// Loop
#define inc(i, a, n) for (ll i = (a), _##i = (n); i <= _##i; ++i)
#define dec(i, a, n) for (ll i = (a), _##i = (n); i >= _##i; --i)
#define rep(i, n) for (ll i = 0, _##i = (n); i < _##i; ++i)
#define each(i, a) for (auto &&i : a)

// Stream
#define fout(n) cout << fixed << setprecision(n)
struct io {
  io() { cin.tie(nullptr), ios::sync_with_stdio(false); }
} io;

// Speed
#pragma GCC optimize("Ofast,unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

// Math
inline constexpr ll gcd(const ll a, const ll b) {
  return b ? gcd(b, a % b) : a;
}
inline constexpr ll lcm(const ll a, const ll b) { return a / gcd(a, b) * b; }

inline constexpr ll modulo(const ll n, const ll m = MOD) {
  ll k = n % m;
  return k + m * (k < 0);
}
inline constexpr ll chmod(ll &n, const ll m = MOD) {
  n %= m;
  return n += m * (n < 0);
}
inline constexpr ll mpow(ll a, ll n, const ll m = MOD) {
  ll r = 1;
  rep(i, 64) {
    if (n & (1LL << i))
      r *= a;
    chmod(r, m);
    a *= a;
    chmod(a, m);
  }
  return r;
}
inline ll inv(const ll n, const ll m = MOD) {
  ll a = n, b = m, x = 1, y = 0;
  while (b) {
    ll t = a / b;
    a -= t * b;
    swap(a, b);
    x -= t * y;
    swap(x, y);
  }
  return modulo(x, m);
}

namespace rollinghash {
using u64 = uint_fast64_t;
using u128 = __uint128_t;
const u64 mo = (1LL << 61) - 1;
const u64 bases[64] = {257, 262, 266, 275, 276, 281, 285, 290, 296, 302, 306,
                       310, 311, 313, 323, 333, 344, 345, 350, 357, 367, 370,
                       373, 402, 423, 425, 431, 440, 442, 443, 454, 457, 458,
                       462, 471, 478, 481, 487, 489, 492, 499, 501, 502, 503,
                       506, 514, 524, 532, 535, 541, 550, 552, 557, 559, 562,
                       563, 567, 570, 571, 580, 592, 597, 604, 612};
random_device rd;
u64 base = bases[rd() & 63];

u64 add(u64 a, u64 b) {
  u64 t = a + b;
  return t >= mo ? t - mo : t;
}
u64 minus(u64 a) { return a == 0 ? 0 : mo - a; }
u64 mul(u64 a, u64 b) {
  u128 t = u128(a) * u128(b);
  t = (t >> 61) + (t & mo);
  return t >= mo ? t - mo : t;
}
template <class T> vector<u64> cast(vector<T> v) {
  return vector<u64>(v.begin(), v.end());
}
vector<u64> cast(string v) { return vector<u64>(v.begin(), v.end()); }

struct rhash {
  vector<u64> data, hash_val, base_pow;
  rhash(vector<u64> v) : data(v) {
    u64 n = data.size();
    hash_val.assign(n + 1, 0);
    base_pow.assign(n + 1, 0);
    base_pow[0] = 1;
    for (u64 i = 0; i < n; i++) {
      hash_val[i + 1] = add(mul(hash_val[i], base), v[i]);
      base_pow[i + 1] = mul(base_pow[i], base);
    }
  }
  u64 operator()(u64 l, u64 r) {
    return add(hash_val[r], minus(mul(hash_val[l], base_pow[r - l])));
  }
  u64 hash_merge(u64 h1, u64 h2, u64 h2len) {
    return add(mul(h1, base_pow[h2len]), h2);
  }

  void push_back(vector<u64> v) {
    u64 n = hash_val.size() - 1, m = v.size();
    hash_val.resize(n + m + 1);
    base_pow.resize(n + m + 1);
    for (u64 i = n; i < n + m; i++) {
      hash_val[i + 1] = add(mul(hash_val[i], base), v[i - n]);
      base_pow[i + 1] = mul(base_pow[i], base);
    }
  }
};

u64 LCP(rhash &a, rhash &b, u64 l1, u64 r1, u64 l2, u64 r2) {
  u64 len = min(r1 - l1, r2 - l2);
  u64 low = -1, high = len + 1;
  while (high - low > 1) {
    u64 mid = (low + high) / 2;
    if (a(l1, l1 + mid) == b(l2, l2 + mid)) {
      low = mid;
    } else {
      high = mid;
    }
  }
  return low;
}
} // namespace rollinghash

signed main() {
  ll N;
  cin >> N;
  string S;
  cin >> S;
  using namespace rollinghash;
  rhash R(cast(S));
  ll res = 0;
  rep(i, N) {
    rep(j, N) {
      if (i >= j)
        continue;
      ll ok = 0, ng = j - i + 1;
      while (ng - ok > 1) {
        ll md = (ok + ng) / 2;
        if (R(i, i + md) == R(j, j + md)) {
          ok = md;
        } else {
          ng = md;
        }
      }
      chmax(res, ok);
    }
  }
  cout << res << rt;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;

// Define
using ll = long long;
using ull = unsigned long long;
using ld = long double;
template <class T> using pvector = vector<pair<T, T>>;
template <class T>
using rpriority_queue = priority_queue<T, vector<T>, greater<T>>;
constexpr const ll dx[4] = {1, 0, -1, 0};
constexpr const ll dy[4] = {0, 1, 0, -1};
constexpr const ll MOD = 1e9 + 7;
constexpr const ll mod = 998244353;
constexpr const ll INF = 1LL << 60;
constexpr const ll inf = 1 << 30;
constexpr const char rt = '\n';
constexpr const char sp = ' ';
#define rt(i, n) (i == (ll)(n)-1 ? rt : sp)
#define len(x) ((ll)(x).size())
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define eb emplace_back
#define ifn(x) if (not(x))
#define elif else if
#define elifn else ifn
#define fi first
#define se second

using graph = vector<vector<ll>>;
template <class T> using wgraph = vector<vector<ll, T>>;
bool __DIRECTED__ = true;
istream &operator>>(istream &is, graph &g) {
  ll a, b;
  is >> a >> b;
  g[a - 1].pb(b - 1);
  if (__DIRECTED__ == false)
    g[b - 1].pb(a - 1);
  return is;
}

template <class T> istream &operator>>(istream &is, wgraph<T> &g) {
  ll a, b;
  T c;
  is >> a >> b >> c;
  g[a - 1].pb({b - 1, c});
  if (__DIRECTED__ == false)
    g[b - 1].pb({a - 1, c});
  return is;
}

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

// Debug
#define debug(...)                                                             \
  {                                                                            \
    cerr << __LINE__ << ": " << #__VA_ARGS__ << " = ";                         \
    for (auto &&X : {__VA_ARGS__})                                             \
      cerr << "[" << X << "] ";                                                \
    cerr << rt;                                                                \
  }

#define dump(a, h, w)                                                          \
  {                                                                            \
    cerr << __LINE__ << ": " << #a << " = [" << rt;                            \
    rep(_i, h) {                                                               \
      rep(_j, w) {                                                             \
        if (abs(a[_i][_j]) >= INF / 2 and a[_i][_j] <= -INF / 2)               \
          cerr << '-';                                                         \
        if (abs(a[_i][_j]) >= INF / 2)                                         \
          cerr << "∞" << sp;                                                   \
        else                                                                   \
          cerr << a[_i][_j] << sp;                                             \
      }                                                                        \
      cerr << rt;                                                              \
    }                                                                          \
    cerr << "]" << rt;                                                         \
  }

#define vdump(a, n)                                                            \
  {                                                                            \
    cerr << __LINE__ << ": " << #a << " = [";                                  \
    rep(_i, n) {                                                               \
      if (_i)                                                                  \
        cerr << sp;                                                            \
      if (abs(a[_i]) >= INF / 2 and a[_i] <= -INF / 2)                         \
        cerr << '-';                                                           \
      if (abs(a[_i]) >= INF / 2)                                               \
        cerr << "∞" << sp;                                                     \
      else                                                                     \
        cerr << a[_i];                                                         \
    }                                                                          \
    cerr << "]" << rt;                                                         \
  }

// Loop
#define inc(i, a, n) for (ll i = (a), _##i = (n); i <= _##i; ++i)
#define dec(i, a, n) for (ll i = (a), _##i = (n); i >= _##i; --i)
#define rep(i, n) for (ll i = 0, _##i = (n); i < _##i; ++i)
#define each(i, a) for (auto &&i : a)

// Stream
#define fout(n) cout << fixed << setprecision(n)
struct io {
  io() { cin.tie(nullptr), ios::sync_with_stdio(false); }
} io;

// Speed
#pragma GCC optimize("Ofast,unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

// Math
inline constexpr ll gcd(const ll a, const ll b) {
  return b ? gcd(b, a % b) : a;
}
inline constexpr ll lcm(const ll a, const ll b) { return a / gcd(a, b) * b; }

inline constexpr ll modulo(const ll n, const ll m = MOD) {
  ll k = n % m;
  return k + m * (k < 0);
}
inline constexpr ll chmod(ll &n, const ll m = MOD) {
  n %= m;
  return n += m * (n < 0);
}
inline constexpr ll mpow(ll a, ll n, const ll m = MOD) {
  ll r = 1;
  rep(i, 64) {
    if (n & (1LL << i))
      r *= a;
    chmod(r, m);
    a *= a;
    chmod(a, m);
  }
  return r;
}
inline ll inv(const ll n, const ll m = MOD) {
  ll a = n, b = m, x = 1, y = 0;
  while (b) {
    ll t = a / b;
    a -= t * b;
    swap(a, b);
    x -= t * y;
    swap(x, y);
  }
  return modulo(x, m);
}

namespace rollinghash {
using u64 = uint_fast64_t;
using u128 = __uint128_t;
const u64 mo = (1LL << 61) - 1;
const u64 bases[64] = {257, 262, 266, 275, 276, 281, 285, 290, 296, 302, 306,
                       310, 311, 313, 323, 333, 344, 345, 350, 357, 367, 370,
                       373, 402, 423, 425, 431, 440, 442, 443, 454, 457, 458,
                       462, 471, 478, 481, 487, 489, 492, 499, 501, 502, 503,
                       506, 514, 524, 532, 535, 541, 550, 552, 557, 559, 562,
                       563, 567, 570, 571, 580, 592, 597, 604, 612};
random_device rd;
u64 base = bases[rd() & 63];

u64 add(u64 a, u64 b) {
  u64 t = a + b;
  return t >= mo ? t - mo : t;
}
u64 minus(u64 a) { return a == 0 ? 0 : mo - a; }
u64 mul(u64 a, u64 b) {
  u128 t = u128(a) * u128(b);
  t = (t >> 61) + (t & mo);
  return t >= mo ? t - mo : t;
}
template <class T> vector<u64> cast(vector<T> v) {
  return vector<u64>(v.begin(), v.end());
}
vector<u64> cast(string v) { return vector<u64>(v.begin(), v.end()); }

struct rhash {
  vector<u64> data, hash_val, base_pow;
  rhash(vector<u64> v) : data(v) {
    u64 n = data.size();
    hash_val.assign(n + 1, 0);
    base_pow.assign(n + 1, 0);
    base_pow[0] = 1;
    for (u64 i = 0; i < n; i++) {
      hash_val[i + 1] = add(mul(hash_val[i], base), v[i]);
      base_pow[i + 1] = mul(base_pow[i], base);
    }
  }
  u64 operator()(u64 l, u64 r) {
    return add(hash_val[r], minus(mul(hash_val[l], base_pow[r - l])));
  }
  u64 hash_merge(u64 h1, u64 h2, u64 h2len) {
    return add(mul(h1, base_pow[h2len]), h2);
  }

  void push_back(vector<u64> v) {
    u64 n = hash_val.size() - 1, m = v.size();
    hash_val.resize(n + m + 1);
    base_pow.resize(n + m + 1);
    for (u64 i = n; i < n + m; i++) {
      hash_val[i + 1] = add(mul(hash_val[i], base), v[i - n]);
      base_pow[i + 1] = mul(base_pow[i], base);
    }
  }
};

u64 LCP(rhash &a, rhash &b, u64 l1, u64 r1, u64 l2, u64 r2) {
  u64 len = min(r1 - l1, r2 - l2);
  u64 low = -1, high = len + 1;
  while (high - low > 1) {
    u64 mid = (low + high) / 2;
    if (a(l1, l1 + mid) == b(l2, l2 + mid)) {
      low = mid;
    } else {
      high = mid;
    }
  }
  return low;
}
} // namespace rollinghash

signed main() {
  ll N;
  cin >> N;
  string S;
  cin >> S;
  using namespace rollinghash;
  rhash R(cast(S));
  ll res = 0;
  rep(i, N) rep(j, N) if (i < j) chmax(res, (ll)LCP(R, R, i, j, j, N));

  cout << res << rt;
}