Radix-2 Iterative-FFT

来源：互联网发布：知乎三国和战国编辑：程序博客网时间：2024/06/03 14:36
#include<bits/stdc++.h>using namespace std;const double PI = acos(-1.0);const int maxn = 300000 + 10;int n, m, base;int c[maxn], rev[maxn];complex<double> a[maxn], b[maxn], p[maxn];int read() {    int n = 0, f = 1;    char ch = getchar();    while(ch < '0' || ch > '9') { if(ch == '-') f = -1; ch = getchar(); }    while(ch >='0' && ch <='9') { n = n * 10 + ch - 48; ch = getchar(); }    return n * f;}void init() {    int dis = 0;    for(base = 1; base <= n + m; base <<= 1) ++dis;    for(int i=0; i<=base; i++)         rev[i] = (rev[i>>1] >> 1) | ((i & 1) << (dis - 1));}void FFT(complex<double> x[], int n, int type) {    for(int i=0; i<n; ++i)         if(i < rev[i]) swap(x[i], x[rev[i]]);    for(int s=1; 1 << s <= n; ++s) {        int m = 1 << s;        complex<double> wm(cos(type * 2 * PI / m), sin(type * 2 * PI / m));        for(int k=0; k < n; k += m) {            complex<double> w(1, 0);            for(int j=0; j < m >> 1; ++j) {                complex<double> u = x[k + j];                complex<double> t = x[k + j + m / 2] * w;                x[k + j] = u + t;                x[k + j + m / 2] = u - t;                w *= wm;            }        }    }}int main() {#ifndef ONLINE_JUDGE    freopen("data.txt", "r", stdin);     freopen("ans.txt", "w", stdout); #endif    scanf("%d%d", &n, &m);     for(int i=0; i<=n; ++i) a[i] = read();     for(int i=0; i<=m; ++i) b[i] = read();     init();    FFT(a, base, 1); FFT(b, base, 1);    for(int i=0; i<base; ++i) p[i] = a[i] * b[i]; FFT(p, base, -1);    for(int i=0; i<n + m + 1; ++i) c[i] = p[i].real() / base + 0.1;    for(int i=0; i<n + m + 1; ++i) printf("%d%c", c[i], i == n + m ? '\n' : ' ');    return 0;}
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