fft模板

#include <cstdio>
#include <algorithm>
#include <cmath> 
#include <complex>
using namespace std;
const int N = 4e6 + 5;
const double pi = acos(-1);
typedef complex<double> cd;
int n, m, l, r[N];
cd a[N], b[N];
void fft(cd *c, int type){
    for(int i = 0; i < n; i++)
    if(i < r[i]) swap(c[i], c[r[i]]);
    for(int i = 1; i < n; i <<= 1){
        cd x(cos(pi / i), type * sin(pi / i));
        for(int j = 0; j < n; j += (i << 1)){
            cd y(1, 0);
            for(int k = 0; k < i; k++, y *= x){
                cd p = c[j + k], q = y * c[i + j + k];
                c[j + k] = p + q, c[i + j + k] = p - q;
            }
        }
    }
}

inline void init(){
    scanf("%d %d", &n, &m);
    for(int i = 0; i <= n; i++) {
        int x; scanf("%d", &x);
        a[i] = x;
    }
    for(int i = 0; i <= m; i++) {
        int x; scanf("%d", &x);
        b[i] = x;
    }
    for(m += n, n = 1; n <= m; n <<= 1) l++;
}

inline void cal(){
    for(int i = 0; i < n; i++)
        r[i] = (r[i >> 1] >> 1) | ((i & 1) << (l - 1));
}

int main(){
    init();
    cal();
    fft(a, 1); fft(b, 1);
    for(int i = 0; i <= n; 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;    
}