bzoj2179

fft裸题 我还没有背下来fft

#include<bits/stdc++.h>
#define pi acos(-1)
using namespace std;
const int N = 300010;
int n, m, L, x;
int r[N];
complex<double> a[N], b[N];
void fft(complex<double> *a, int f)
{
    for(int i = 0; i < n; ++i) if(i < r[i]) swap(a[i], a[r[i]]);
    for(int i = 1; i < n; i <<= 1)
    {
        complex<double> t(cos(pi / i), f * sin(pi / i));
        for(int p = i << 1, j = 0; j < n; j += p)
        {
            complex<double> w(1, 0);
            for(int k = 0; k < i; ++k, w *= t)
            {
                complex<double> x = a[j + k], y = w * a[j + k + i];
                a[j + k] = x + y; a[j + k + i] = x - y;
            }
        } 
    } 
}
int main()
{
    scanf("%d%d", &n, &m);
    for(int i = 0; i <= n; ++i) scanf("%d", &x), a[i] = x;
    for(int i = 0; i <= m; ++i) scanf("%d", &x), b[i] = x;
    m = n + m; for(n = 1; n <= m; n <<= 1) ++L;
    for(int i = 0; i < n; ++i) r[i] = (r[i >> 1] >> 1) | ((i & 1) << (L - 1));
    fft(a, 1); fft(b, 1);
    for(int i = 0; i <= n; ++i) a[i] = a[i] * b[i];
    fft(a, -1);
    for(int i = 0; i <= m; ++i) printf("%d ", (int)(a[i].real() / n + 0.5));
    return 0;
}