Problem p00451 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef tuple<int, int> duo;
const int dx[] = {0, 0, 1, -1, 1, 1, -1, -1};
const int dy[] = {1, -1, 0, 0, 1, -1, 1, -1};
const int Mod = 1000000000 + 0;
//{{{ templates
#define TT_ template <typename T> inline
#define TTF_ template <typename T, typename F> inline
TT_ T sq(T x) { return x * x; }
TT_ T In() {
  T x;
  cin >> x;
  return x;
}
TT_ void Out(T &x) { cout << x; }
TT_ void sort(T &v) { sort(begin(v), end(v)); }
TT_ void revs(T &v) { reverse(begin(v), end(v)); }
TT_ void uniq(T &v) {
  sort(v);
  v.erase(unique(begin(v), end(v)), end(v));
}
TT_ int ubnd(T &v, typename T::value_type &x) {
  return upper_bound(begin(v), end(v), x) - begin(v);
}
TT_ int lbnd(T &v, typename T::value_type &x) {
  return lower_bound(begin(v), end(v), x) - begin(v);
}
TTF_ void inpt(T &v, int n, F f) {
  for (v.reserve(n); n--; v.emplace_back(f()))
    ;
}
TTF_ void show(T &v, F f, string d = " ", string e = "\\n") {
  int i = 0;
  for (auto &x : v)
    i++ && (cout << d), f(x);
  cout << e;
}
TT_ typename T::iterator minel(T &v) { return min_element(begin(v), end(v)); }
TT_ typename T::iterator maxel(T &v) { return max_element(begin(v), end(v)); }

inline void fast_io() {
  ios::sync_with_stdio(0);
  cin.tie(0);
}
inline int in() {
  int x;
  scanf("%d", &x);
  return x;
}
inline ll pow_mod(ll a, ll k, ll m) {
  ll r = 1;
  for (; k > 0; a = a * a % m, k >>= 1)
    if (k & 1)
      r = r * a % m;
  return r;
}
inline ll mod_inv(ll a, ll p) { return pow_mod(a, p - 2, p); }
//}}} priority_queue queue deque front stringstream max_element min_element
//insert count make_tuple

void z_algo(const string &s, vector<int> &z) {
  const int n = s.size();
  z.assign(n, 0);
  int R, L;
  R = L = 0;
  for (int i = 1; i < n; i++) {
    if (i > R) {
      L = R = i;
      while (R < n && s[R - L] == s[R])
        R++;
      z[i] = R - L;
      R--;
    } else {
      int k = i - L;
      if (z[k] < R - i + 1)
        z[i] = z[k];
      else {
        L = i;
        while (R < n && s[R - L] == s[R])
          R++;
        z[i] = R - L;
        R--;
      }
    }
  }
}

int main() {
  string s, t;
  while (cin >> s >> t) {
    const string S = s + '$' + t;
    const int sl = s.size();
    int maxi = 0;
    for (int i = 0; i < sl; i++) {
      vector<int> z;
      z_algo(S.substr(i), z);
      maxi = max(maxi, *max_element(begin(z) + (sl - i), end(z)));
    }
    cout << maxi << endl;
  }
  return 0;
}

Error: TLE

Fixed submission:

#include <bits/stdc++.h>

using namespace std;

struct RollingHash {
  typedef unsigned long long hash_t;
  static const hash_t P = 1469979569;
  const int n;
  vector<hash_t> pow, phash;
  RollingHash(const string &s) : n(s.size()), pow(n + 1), phash(n + 1) {
    pow[0] = 1;
    phash[0] = 0;
    for (int i = 0; i < n; i++) {
      phash[i + 1] = s[i] + phash[i] * P;
      pow[i + 1] = pow[i] * P;
    }
  }
  hash_t hash(int i, int j) { return phash[j] - phash[i] * pow[j - i]; }
  int lcp(int i, int j) {
    int l = 0, r = min(n - i, n - j) + 1;
    while (r - l > 1) {
      int m = r + l >> 1;
      if (hash(i, i + m) == hash(j, j + m))
        l = m;
      else
        r = m;
    }
    return l;
  }
};

typedef long long ll;
typedef long double ld;
typedef tuple<int, int> duo;
const int dx[] = {0, 0, 1, -1, 1, 1, -1, -1};
const int dy[] = {1, -1, 0, 0, 1, -1, 1, -1};
const int Mod = 1000000000 + 0;
//{{{ templates
#define TT_ template <typename T> inline
#define TTF_ template <typename T, typename F> inline
TT_ T sq(T x) { return x * x; }
TT_ T In() {
  T x;
  cin >> x;
  return x;
}
TT_ void Out(T &x) { cout << x; }
TT_ void sort(T &v) { sort(begin(v), end(v)); }
TT_ void revs(T &v) { reverse(begin(v), end(v)); }
TT_ void uniq(T &v) {
  sort(v);
  v.erase(unique(begin(v), end(v)), end(v));
}
TT_ int ubnd(T &v, typename T::value_type &x) {
  return upper_bound(begin(v), end(v), x) - begin(v);
}
TT_ int lbnd(T &v, typename T::value_type &x) {
  return lower_bound(begin(v), end(v), x) - begin(v);
}
TTF_ void inpt(T &v, int n, F f) {
  for (v.reserve(n); n--; v.emplace_back(f()))
    ;
}
TTF_ void show(T &v, F f, string d = " ", string e = "\\n") {
  int i = 0;
  for (auto &x : v)
    i++ && (cout << d), f(x);
  cout << e;
}
TT_ typename T::iterator minel(T &v) { return min_element(begin(v), end(v)); }
TT_ typename T::iterator maxel(T &v) { return max_element(begin(v), end(v)); }

inline void fast_io() {
  ios::sync_with_stdio(0);
  cin.tie(0);
}
inline int in() {
  int x;
  scanf("%d", &x);
  return x;
}
inline ll pow_mod(ll a, ll k, ll m) {
  ll r = 1;
  for (; k > 0; a = a * a % m, k >>= 1)
    if (k & 1)
      r = r * a % m;
  return r;
}
inline ll mod_inv(ll a, ll p) { return pow_mod(a, p - 2, p); }
//}}} priority_queue queue deque front stringstream max_element min_element
//insert count make_tuple

int main() {
  string s, t;
  while (cin >> s >> t) {
    string S = s + '$' + t;
    RollingHash rh(S);
    int maxi = 0;
    for (int i = 0; i < s.size(); i++) {
      for (int j = 0; j < t.size(); j++) {
        maxi = max(maxi, rh.lcp(i, s.size() + 1 + j));
      }
    }
    cout << maxi << endl;
  }
  return 0;
}