MultisetHash.hpp

using ull = unsigned long long;
random_device rnd;
mt19937 mt(rnd());
mt19937_64 mt64(rnd());
int mod_pow(int x, int n, int mod) {
    if (n <= 0) return 1;
    int tmp = mod_pow(x, n / 2, mod);
    return tmp * tmp % mod * (n % 2 ? x : 1) % mod;
}
// Miller-Rabin
bool is_prime(int n, int times = 50) {
    if (n == 2) return true;
    if (n % 2 == 0 || n < 2) return false;
    int d = n - 1;
    while (d % 2 == 0) d /= 2;
    while (times--) {
        int a = rnd() % (n - 2) + 1;
        int t = d;
        int y = mod_pow(a, t, n);
        while (t != n - 1 && y != 1 && y != n - 1) {
            y = y * y % n;
            t *= 2;
        }
        if (y != n - 1 && t % 2 == 0) {
            return false;
        }
    }
    return true;
}
int gen_prime() {
    int cnt = 0;
    while (1) {
        int n = mt();
        n != 1;
        if (is_prime(n)) return n;
    }
}
class MultisetHash {
public:
    vector<ull> hash, pows;
    ull mod;
    int to_int(char c) { return c - 'a'; }
    MultisetHash() {}
    MultisetHash(const string& S, int k = 26, ull base = gen_prime(), ull m = gen_prime())
        : hash(S.size() + 1), pows(k), mod(m) {
        pows[0] = 1;
        for (int i = 0; i < k - 1; i++) {
            pows[i + 1] = pows[i] * base % mod;
        }
        for (int i = 0; i < S.size(); i++) {
            hash[i + 1] = hash[i] + pows[to_int(S[i])];
        }
    }
    // [l, r)
    ull get(int l, int r) {
        int ret = hash[r] + mod - hash[l];
        if (ret >= mod) ret -= mod;
        return ret;
    }
};