bzoj 2194

FFT;把b数组倒过来就好看了

#include<bits/stdc++.h>#define rep(i,k,n) for(int i=k;i<(n);i++)using namespace std;typedef double db;const int maxn = (1 << 20) + 5;const db pi = acos(-1.0);struct virt {    db r, i;    virt(db r = 0.0, db i = 0.0): r(r), i(i) {}};virt operator+(virt a, virt b) {    return virt(a.r + b.r, a.i + b.i);}virt operator-(virt a, virt b) {    return virt(a.r - b.r, a.i - b.i);}virt operator*(virt a, virt b) {    return virt(a.r * b.r - a.i * b.i, a.i * b.r + a.r * b.i);}virt a[maxn], b[maxn];int n, m, L = 0, rev[maxn], cn;void fft(virt* x, int op) {    rep(i, 1, n)if(rev[i] > i)swap(x[rev[i]], x[i]);    for(int h = 2; h <= n; h <<= 1) {        virt wn = virt(cos(op * 2 * pi / h), sin(op * 2 * pi / h));        for(int j = 0; j < n; j += h) {            virt w = virt(1.0, 0.0);            for(int k = j; k < j + h / 2; k++) {                virt p = x[k];                virt q = w * x[k + h / 2];                x[k] = p + q;                x[k + h / 2] = p - q;                w = w * wn;            }        }    }    if(op == -1)rep(i, 0, n)x[i].r /= n;   }int main() {    //freopen("in.in", "r", stdin);    scanf("%d", &n);    cn = n;    rep(i, 0, n) {        scanf("%lf%lf", &a[i].r, &b[n - i - 1].r);        a[i].i = b[n - 1 - i].i = 0.0;    }    m = n << 1;    for(n = 1; n <= m; n <<= 1)L++;    rep(i, 0, n)rev[i] = (rev[i >> 1] >> 1) | ((i & 1) << (L - 1));    fft(a, 1);    fft(b, 1);    rep(i, 0, n + 1)a[i] = a[i] * b[i];    fft(a, -1);    rep(i, cn - 1, 2 * cn - 1)printf("%d\n", (int)(a[i].r + 0.1));    return 0;}