Luogu4191:[CTSC2010]效能優化
阿新 • • 發佈:2019-01-02
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題目翻譯:給定兩個 \(n\) 次多項式 \(A,B\) 和一個整數 \(C\),求 \(A\times B^C\) 在模 \(x^n\) 意義下的卷積
顯然就是個迴圈卷積,所以只要代入 \(\omega_n^{k}\) 進去求出點值,然後插值就好了
???\(n\) 不是 \(2^k\) 的形式,不能直接 \(NTT\)
怎麼辦呢?
根據題目性質,可以把 \(n\) 拆成 \(2^{a_1}3^{a_2}5^{a_3}7^{a_4}\) 的形式
這啟示我們每次不是每次分成兩半而是拆分成 \(3/5/7\) 次,然後再合併點值
設 \(F(x)=\sum a_ix^i,F_r(x)=\sum a_{ip+r}x^i\)
那麼 \(F(x)=\sum x^rF(x^p)\)
根據單位複數的性質(消去引理和折半引理)那麼
\[F(\omega_n^{an+b})=\sum \omega_{np}^{(an+b)r}F_r(w_n^b)\]
那麼只需要寫一個每次分 \(p\) 份的 \(FFT\) 就好了
# include <bits/stdc++.h> using namespace std; typedef long long ll; const int maxn(5e5 + 5); int n, c, a[maxn], b[maxn], tmp[maxn], g, pri[233333], tot, pw[2][maxn], mod, r[maxn]; inline int Pow(ll x, int y) { register ll ret = 1; for (; y; y >>= 1, x = x * x % mod) if (y & 1) ret = ret * x % mod; return ret; } inline void Inc(int &x, int y) { x = x + y >= mod ? x + y - mod : x + y; } int Dfs(int s, int p, int cur, int blk) { if (cur == tot + 1) return s + p; register int nxt; nxt = blk / pri[cur]; return Dfs(s + nxt * (p % pri[cur]), (p - p % pri[cur]) / pri[cur], cur + 1, nxt); } inline void DFT(int *p, int opt) { register int i, j, k, l, q, t, cur; for (i = 0; i < n; ++i) tmp[r[i]] = p[i]; for (i = 0; i < n; ++i) p[i] = tmp[i], tmp[i] = 0; for (i = 1, cur = tot; i < n; i *= pri[cur], --cur) { for (t = i * pri[cur], j = 0; j < n; j += t) for (k = 0; k < t; k += i) for (l = 0; l < i; ++l) for (q = 0; q < pri[cur]; ++q) Inc(tmp[j + k + l], (ll)pw[opt == -1][n / t * (k + l) * q % n] * p[j + i * q + l] % mod); for (j = 0; j < n; ++j) p[j] = tmp[j], tmp[j] = 0; } if (opt == -1) for (c = Pow(n, mod - 2), i = 0; i < n; ++i) p[i] = (ll)p[i] * c % mod; } int main() { register int i, j, x; scanf("%d%d", &n, &c), mod = n + 1; for (x = n, i = 2; i * i <= x; ++i) while (x % i == 0) pri[++tot] = i, x /= i; if (x > 1) pri[++tot] = x; for (i = 2; ; ++i) { for (g = i, j = 1; g && j <= tot; ++j) if (Pow(g, n / pri[j]) == 1) g = 0; if (g) break; } for (i = 0; i < n; ++i) scanf("%d", &a[i]); for (i = 0; i < n; ++i) scanf("%d", &b[i]); pw[0][0] = pw[1][0] = 1, pw[0][1] = g, pw[1][1] = Pow(g, mod - 2); for (i = 2; i < n; ++i) pw[0][i] = (ll)pw[0][i - 1] * g % mod, pw[1][i] = (ll)pw[1][i - 1] * pw[1][1] % mod; for (i = 0; i < n; ++i) r[i] = Dfs(0, i, 1, n); DFT(a, 1), DFT(b, 1); for (i = 0; i < n; ++i) a[i] = (ll)a[i] * Pow(b[i], c) % mod; DFT(a, -1); for (i = 0; i < n; ++i) printf("%d\n", a[i]); return 0; }