Rolling Hash

// Warning: Change mod and N according to question
const int mod = (1LL << 31)-1;
const int N = 1e6 + 3;

#define int long long
#define MP make_pair
#define F first
#define S second
#define sz(s) ((int)s.size())

int rand(int l, int r){
  static std::mt19937 rng(std::chrono::steady_clock::now().time_since_epoch().count());
  std::uniform_int_distribution<int> ludo(l, r); return ludo(rng);
}

inline int add(int x, int y, int mod = ::mod) {
  x += y;
  if (x >= mod or x < 0) x %= mod;
  if (x >= 0) return x;
  return x + mod;
}
inline int mul(int x, int y, int mod = ::mod) {
  if (x >= mod or x + mod < 0) x %= mod;
  if (y >= mod or y + mod < 0) y %= mod;
  x *= y;
  if (x >= mod or x + mod < 0) x %= mod;
  if (x >= 0) return x;
  return x + mod;
}
inline int sub(int x, int y, int mod = ::mod) {
  x -= y;
  if (x + mod < 0 or x >= mod) {
    x %= mod;
  }
  if (x >= 0) return x;
  return x + mod;
}

char s[N];

struct Hash {
  vector<pair<int,int>> H, pre;
  Hash(const char *s, int N, int b1 = 41, int b2 = 53) :
    H(N + 5), pre(N + 5) {
    pre[0].F = 1, b1 = rand(37, 1 << 10);
    pre[0].S = 1, b2 = rand(41, 1 << 9);
    int cur1 = 0, cur2 = 0;
    for (int i = 1; i <= N; ++i) {
      pre[i].F = mul(pre[i-1].F, b1);
      pre[i].S = mul(pre[i-1].S, b2);
      cur1 = add(mul(cur1, b1), (s[i] - 'a' + 1));
      cur2 = add(mul(cur2, b2), (s[i] - 'a' + 1));
      H[i].F = cur1, H[i].S = cur2;
    }
  }
  pair<int,int> get_hash(int l, int r) {
    int rem1 = mul(pre[r-l+1].F, H[l-1].F);
    int rem2 = mul(pre[r-l+1].S, H[l-1].S);
    return MP(sub(H[r].F, rem1), sub(H[r].S, rem2));
  }
};