Problem p02913 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
// typedef
//-------------------------#include <bits/stdc++.h>

const double pi = 3.141592653589793238462643383279;

using namespace std;

template <typename T = int> inline T readT() {
  char c = getchar_unlocked();
  bool neg = (c == '-');
  T res = neg ? 0 : c - '0';
  while (isdigit(c = getchar_unlocked()))
    res = res * 10 + c - '0';
  return neg ? -res : res;
}
template <typename T = int> inline void writeT(T x, char c = '\n') {
  int d[20], i = 0;
  if (x < 0)
    putchar_unlocked('-'), x *= -1;
  do {
    d[i++] = x % 10;
  } while (x /= 10);
  while (i--)
    putchar_unlocked('0' + d[i]);
  putchar_unlocked(c);
}

// typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<long long, long long> PLL;
typedef pair<int, PII> TIII;
typedef long long LL;
typedef unsigned long long ULL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;

// container util

//------------------------------------------
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define SQ(a) ((a) * (a))
#define EACH(i, c)                                                             \
  for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define EXIST(s, e) ((s).find(e) != (s).end())
#define SORT(c) sort((c).begin(), (c).end())

// repetition
//------------------------------------------
#define FOR(i, s, n) for (int i = s; i < (int)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define MOD 1000000007

#define rep(i, a, b) for (int i = a; i < (b); ++i)
#define trav(a, x) for (auto &a : x)
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
const double EPS = 1E-8;

#define chmin(x, y) x = min(x, y)
#define chmax(x, y) x = max(x, y)

class UnionFind {
public:
  vector<int> par;
  vector<int> siz;

  UnionFind(int sz_) : par(sz_), siz(sz_, 1) {
    for (ll i = 0; i < sz_; ++i)
      par[i] = i;
  }
  void init(int sz_) {
    par.resize(sz_);
    siz.assign(sz_, 1LL);
    for (ll i = 0; i < sz_; ++i)
      par[i] = i;
  }

  int root(int x) {
    while (par[x] != x) {
      x = par[x] = par[par[x]];
    }
    return x;
  }

  bool merge(int x, int y) {
    x = root(x);
    y = root(y);
    if (x == y)
      return false;
    if (siz[x] < siz[y])
      swap(x, y);
    siz[x] += siz[y];
    par[y] = x;
    return true;
  }

  bool issame(int x, int y) { return root(x) == root(y); }

  int size(int x) { return siz[root(x)]; }
};

ll modPow(ll x, ll n, ll mod = MOD) {
  ll res = 1;
  while (n) {
    if (n & 1)
      res = (res * x) % mod;

    res %= mod;
    x = x * x % mod;
    n >>= 1;
  }
  return res;
}

#define SIEVE_SIZE 5000000 + 10
bool sieve[SIEVE_SIZE];
void makeSieve() {
  for (int i = 0; i < SIEVE_SIZE; ++i)
    sieve[i] = true;
  sieve[0] = sieve[1] = false;
  for (int i = 2; i * i < SIEVE_SIZE; ++i)
    if (sieve[i])
      for (int j = 2; i * j < SIEVE_SIZE; ++j)
        sieve[i * j] = false;
}

bool isprime(ll n) {
  if (n == 0 || n == 1)
    return false;
  for (ll i = 2; i * i <= n; ++i)
    if (n % i == 0)
      return false;
  return true;
}

const int MAX = 2000010;
long long fac[MAX], finv[MAX], inv[MAX];

// テーブルを作る前処理
void COMinit() {
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < MAX; i++) {
    fac[i] = fac[i - 1] * i % MOD;
    inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
    finv[i] = finv[i - 1] * inv[i] % MOD;
  }
}

// 二項係数計算
long long COM(int n, int k) {
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}

long long extGCD(long long a, long long b, long long &x, long long &y) {
  if (b == 0) {
    x = 1;
    y = 0;
    return a;
  }
  long long d = extGCD(b, a % b, y, x);
  y -= a / b * x;
  return d;
}
// 負の数にも対応した mod (a = -11 とかでも OK)
inline long long mod(long long a, long long m) { return (a % m + m) % m; }

// 逆元計算 (ここでは a と m が互いに素であることが必要)
long long modinv(long long a, long long m) {
  long long x, y;
  extGCD(a, m, x, y);
  return mod(x, m); // 気持ち的には x % m だが、x が負かもしれないので
}
ll GCD(ll a, ll b) {

  if (b == 0)
    return a;
  return GCD(b, a % b);
}

typedef vector<ll> vec;
typedef vector<vec> mat;

mat mul(mat &A, mat &B) {
  mat C(A.size(), vec((int)B[0].size()));
  for (int i = 0; i < A.size(); ++i) {
    for (int k = 0; k < B.size(); ++k) {
      for (int j = 0; j < B[0].size(); ++j) {
        C[i][j] = (C[i][j] + A[i][k] * B[k][j] % MOD) % MOD;
      }
    }
  }
  return C;
}
mat matPow(mat A, ll n) {
  mat B(A.size(), vec((int)A.size()));

  for (int i = 0; i < A.size(); ++i) {
    B[i][i] = 1;
  }

  while (n > 0) {
    if (n & 1)
      B = mul(B, A);
    A = mul(A, A);
    n >>= 1;
  }
  return B;
}

map<ll, ll> prime_factor(ll n) {
  map<ll, ll> res;
  for (ll i = 2; i * i <= n; i++) {
    while (n % i == 0) {
      res[i]++;
      n /= i;
    }
  }

  if (n != 1)
    res[n] = 1;
  return res;
}
using ld = long double;
template <typename T = int> struct BIT {
  vector<T> node;

  int N;
  BIT(int n) {
    N = n;
    node.resize(N + 1);
  }

  void add(int i, T x) {
    i++;
    while (i <= N) {
      node[i] += x;
      i += (i & -i);
    }
  }

  T sum(int i) {
    T res = 0;
    while (i > 0) {
      res += node[i];
      i -= (i & -i);
    }
    return res;
  }
};

struct RollingHash {

  using ull = unsigned long long;
  const ull mod = (1UL << 61) - 1;
  const ull MASK30 = (1UL << 30) - 1;
  const ull MASK31 = (1UL << 31) - 1;

  const ull MASK61 = mod;

  ull base;
  int n;
  vector<ull> hash, pow;

  RollingHash(string s) {
    random_device rnd;
    mt19937_64 mt(rnd());
    base = calc_mod(mt()) % 100000 + 1000;

    n = (int)s.size();
    hash.assign(n + 1, 0);
    pow.assign(n + 1, 1);

    for (int i = 0; i < n; i++) {
      hash[i + 1] = calc_mod(mul(hash[i], base) + s[i]);
      pow[i + 1] = calc_mod(mul(pow[i], base));
    }
  }

  ull calc_mod(ull x) {
    ull xu = x >> 61;
    ull xd = x & MASK61;
    ull res = xu + xd;
    if (res >= mod)
      res -= mod;
    return res;
  }

  ull mul(ull a, ull b) {
    ull au = a >> 31;
    ull ad = a & MASK31;
    ull bu = b >> 31;
    ull bd = b & MASK31;
    ull mid = ad * bu + au * bd;
    ull midu = mid >> 30;
    ull midd = mid & MASK30;
    return calc_mod(au * bu * 2 + midu + (midd << 31) + ad * bd);
  }

  //[l,r)のハッシュ値
  inline ull get(int l, int r) {
    ull res = calc_mod(hash[r] + mod * 4 - mul(hash[l], pow[r - l]));
    return res;
  }

  // string tのハッシュ値
  inline ull get(string t) {
    ull res = 0;
    for (int i = 0; i < t.size(); i++) {
      res = calc_mod(mul(res, base) + t[i]);
    }
    return res;
  }

  // string s中のtの数をcount
  inline int count(string t) {
    if (t.size() > n)
      return 0;
    auto hs = get(t);
    int res = 0;
    for (int i = 0; i < n - t.size() + 1; i++) {
      if (get(i, i + t.size()) == hs)
        res++;
    }
    return res;
  }

  // LCPを求める S[a:] T[b:]
  inline int LCP(int a, int b) {
    int len = min((int)hash.size() - a, (int)hash.size() - b);

    int lb = -1, ub = len + 1;
    while (ub - lb > 1) {
      int mid = (lb + ub) / 2;

      if (get(a, a + mid) == get(b, b + mid))
        lb = mid;
      else
        ub = mid;
    }
    return lb;
  }
};
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(5);

  int N;
  string s;
  cin >> N >> s;

  RollingHash rh(s);

  int ans = 0;
  for (int i = 0; i < N; i++) {

    for (int j = i + 1; j < N; j++) {

      ans = max(ans, min(rh.LCP(i, j), j - i));
    }
  }

  cout << ans << endl;
  return 0;
}


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

const double pi = 3.141592653589793238462643383279;

using namespace std;

template <typename T = int> inline T readT() {
  char c = getchar_unlocked();
  bool neg = (c == '-');
  T res = neg ? 0 : c - '0';
  while (isdigit(c = getchar_unlocked()))
    res = res * 10 + c - '0';
  return neg ? -res : res;
}
template <typename T = int> inline void writeT(T x, char c = '\n') {
  int d[20], i = 0;
  if (x < 0)
    putchar_unlocked('-'), x *= -1;
  do {
    d[i++] = x % 10;
  } while (x /= 10);
  while (i--)
    putchar_unlocked('0' + d[i]);
  putchar_unlocked(c);
}

// typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<long long, long long> PLL;
typedef pair<int, PII> TIII;
typedef long long LL;
typedef unsigned long long ULL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;

// container util

//------------------------------------------
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define SQ(a) ((a) * (a))
#define EACH(i, c)                                                             \
  for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define EXIST(s, e) ((s).find(e) != (s).end())
#define SORT(c) sort((c).begin(), (c).end())

// repetition
//------------------------------------------
#define FOR(i, s, n) for (int i = s; i < (int)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define MOD 1000000007

#define rep(i, a, b) for (int i = a; i < (b); ++i)
#define trav(a, x) for (auto &a : x)
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
const double EPS = 1E-8;

#define chmin(x, y) x = min(x, y)
#define chmax(x, y) x = max(x, y)

class UnionFind {
public:
  vector<int> par;
  vector<int> siz;

  UnionFind(int sz_) : par(sz_), siz(sz_, 1) {
    for (ll i = 0; i < sz_; ++i)
      par[i] = i;
  }
  void init(int sz_) {
    par.resize(sz_);
    siz.assign(sz_, 1LL);
    for (ll i = 0; i < sz_; ++i)
      par[i] = i;
  }

  int root(int x) {
    while (par[x] != x) {
      x = par[x] = par[par[x]];
    }
    return x;
  }

  bool merge(int x, int y) {
    x = root(x);
    y = root(y);
    if (x == y)
      return false;
    if (siz[x] < siz[y])
      swap(x, y);
    siz[x] += siz[y];
    par[y] = x;
    return true;
  }

  bool issame(int x, int y) { return root(x) == root(y); }

  int size(int x) { return siz[root(x)]; }
};

ll modPow(ll x, ll n, ll mod = MOD) {
  ll res = 1;
  while (n) {
    if (n & 1)
      res = (res * x) % mod;

    res %= mod;
    x = x * x % mod;
    n >>= 1;
  }
  return res;
}

#define SIEVE_SIZE 5000000 + 10
bool sieve[SIEVE_SIZE];
void makeSieve() {
  for (int i = 0; i < SIEVE_SIZE; ++i)
    sieve[i] = true;
  sieve[0] = sieve[1] = false;
  for (int i = 2; i * i < SIEVE_SIZE; ++i)
    if (sieve[i])
      for (int j = 2; i * j < SIEVE_SIZE; ++j)
        sieve[i * j] = false;
}

bool isprime(ll n) {
  if (n == 0 || n == 1)
    return false;
  for (ll i = 2; i * i <= n; ++i)
    if (n % i == 0)
      return false;
  return true;
}

const int MAX = 2000010;
long long fac[MAX], finv[MAX], inv[MAX];

// テーブルを作る前処理
void COMinit() {
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < MAX; i++) {
    fac[i] = fac[i - 1] * i % MOD;
    inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
    finv[i] = finv[i - 1] * inv[i] % MOD;
  }
}

// 二項係数計算
long long COM(int n, int k) {
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}

long long extGCD(long long a, long long b, long long &x, long long &y) {
  if (b == 0) {
    x = 1;
    y = 0;
    return a;
  }
  long long d = extGCD(b, a % b, y, x);
  y -= a / b * x;
  return d;
}
// 負の数にも対応した mod (a = -11 とかでも OK)
inline long long mod(long long a, long long m) { return (a % m + m) % m; }

// 逆元計算 (ここでは a と m が互いに素であることが必要)
long long modinv(long long a, long long m) {
  long long x, y;
  extGCD(a, m, x, y);
  return mod(x, m); // 気持ち的には x % m だが、x が負かもしれないので
}
ll GCD(ll a, ll b) {

  if (b == 0)
    return a;
  return GCD(b, a % b);
}

typedef vector<ll> vec;
typedef vector<vec> mat;

mat mul(mat &A, mat &B) {
  mat C(A.size(), vec((int)B[0].size()));
  for (int i = 0; i < A.size(); ++i) {
    for (int k = 0; k < B.size(); ++k) {
      for (int j = 0; j < B[0].size(); ++j) {
        C[i][j] = (C[i][j] + A[i][k] * B[k][j] % MOD) % MOD;
      }
    }
  }
  return C;
}
mat matPow(mat A, ll n) {
  mat B(A.size(), vec((int)A.size()));

  for (int i = 0; i < A.size(); ++i) {
    B[i][i] = 1;
  }

  while (n > 0) {
    if (n & 1)
      B = mul(B, A);
    A = mul(A, A);
    n >>= 1;
  }
  return B;
}

map<ll, ll> prime_factor(ll n) {
  map<ll, ll> res;
  for (ll i = 2; i * i <= n; i++) {
    while (n % i == 0) {
      res[i]++;
      n /= i;
    }
  }

  if (n != 1)
    res[n] = 1;
  return res;
}
using ld = long double;
template <typename T = int> struct BIT {
  vector<T> node;

  int N;
  BIT(int n) {
    N = n;
    node.resize(N + 1);
  }

  void add(int i, T x) {
    i++;
    while (i <= N) {
      node[i] += x;
      i += (i & -i);
    }
  }

  T sum(int i) {
    T res = 0;
    while (i > 0) {
      res += node[i];
      i -= (i & -i);
    }
    return res;
  }
};

struct RollingHash {

  using ull = unsigned long long;
  const ull mod = (1UL << 61) - 1;
  const ull MASK30 = (1UL << 30) - 1;
  const ull MASK31 = (1UL << 31) - 1;

  const ull MASK61 = mod;

  ull base;
  int n;
  vector<ull> hash, pow;

  RollingHash(string s) {
    random_device rnd;
    mt19937_64 mt(rnd());
    base = calc_mod(mt()) % 100000 + 1000;

    n = (int)s.size();
    hash.assign(n + 1, 0);
    pow.assign(n + 1, 1);

    for (int i = 0; i < n; i++) {
      hash[i + 1] = calc_mod(mul(hash[i], base) + s[i]);
      pow[i + 1] = calc_mod(mul(pow[i], base));
    }
  }

  ull calc_mod(ull x) {
    ull xu = x >> 61;
    ull xd = x & MASK61;
    ull res = xu + xd;
    if (res >= mod)
      res -= mod;
    return res;
  }

  ull mul(ull a, ull b) {
    ull au = a >> 31;
    ull ad = a & MASK31;
    ull bu = b >> 31;
    ull bd = b & MASK31;
    ull mid = ad * bu + au * bd;
    ull midu = mid >> 30;
    ull midd = mid & MASK30;
    return calc_mod(au * bu * 2 + midu + (midd << 31) + ad * bd);
  }

  //[l,r)のハッシュ値
  inline ull get(int l, int r) {
    ull res = calc_mod(hash[r] + mod * 4 - mul(hash[l], pow[r - l]));
    return res;
  }

  // string tのハッシュ値
  inline ull get(string t) {
    ull res = 0;
    for (int i = 0; i < t.size(); i++) {
      res = calc_mod(mul(res, base) + t[i]);
    }
    return res;
  }

  // string s中のtの数をcount
  inline int count(string t) {
    if (t.size() > n)
      return 0;
    auto hs = get(t);
    int res = 0;
    for (int i = 0; i < n - t.size() + 1; i++) {
      if (get(i, i + t.size()) == hs)
        res++;
    }
    return res;
  }

  // LCPを求める S[a:] T[b:]
  inline int LCP(int a, int b) {
    int len = min((int)hash.size() - a, (int)hash.size() - b);

    int lb = -1, ub = len + 1;
    while (ub - lb > 1) {
      int mid = (lb + ub) / 2;

      if (get(a, a + mid) == get(b, b + mid))
        lb = mid;
      else
        ub = mid;
    }
    return lb;
  }
};
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(5);

  int N;
  string s;
  cin >> N >> s;

  RollingHash rh(s);

  auto check = [&](int d) -> bool {
    map<unsigned long long, unsigned long long> prev;
    for (int i = 0; i + d <= N; i++) {
      auto aba = rh.get(i, i + d);
      if (prev.count(aba)) {
        if (i - prev[aba] >= d)
          return true;
      } else
        prev[aba] = i;
    }
    return false;
  };
  int lb = 0, ub = N / 2 + 1;
  while (ub - lb > 1) {
    int mid = (lb + ub) >> 1;
    if (check(mid))
      lb = mid;
    else
      ub = mid;
  }

  cout << lb << endl;
  return 0;
}