代码

#include <algorithm>

const int N = 1 << 21; const int _N = N >> 1;
const int p = 81 << 21 | 1;
const int _g = 154249541;
const int _h = 5446305;

inline int pow_modp(int a, int b) { int x = 1; for(; b; a = (long long)a * a % p, b >>= 1) if(b & 1) x = (long long)x * a % p; return x; }

unsigned ntt_sup[N];
inline void ntt(auto a[], const int _g) {
	auto b = ntt_sup, j = a, _j = a; int _n = N >> 1, i, k, _k, w, _w;
	for(i = 1, w = _g; i < N; i <<= 1, w = (long long)w * w % p, std :: swap(a, b))
		for(k = 0, j = a, _j = a + _n, _w = 1; k != N; k += i, _w = (long long)_w * w % p)
			for(_k = k, k += i; _k != k; ++j, ++_j, ++_k)
				b[_k] = *j + *_j < p ? *j + *_j : *j + *_j - p,
				b[_k + i] = (long long)(*j - *_j + p) * _w % p;
}

unsigned a[N], b[N];
void poly_multiply(unsigned *aa, int n, unsigned *bb, int m, unsigned *c) {
	std :: copy(aa, aa + n + 1, a), std :: copy(bb, bb + m + 1, b);
	m += n; for(n = 1; n <= m; n <<= 1); ++m;
	ntt(a, _g), ntt(b, _g);     for(int i = 0; i < n; ++i) a[i] = (long long)a[i] * b[i] % p; ntt(a, _h);
	int inv_n = pow_modp(n, p - 2); for(int i = 0; i < m; ++i) c[i] = (long long)a[i] * inv_n % p;
}

评测结果