FFT模板

代码（p3803）

#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<algorithm>
#include<cctype>
#include<cmath>
#include<cstdlib>
#include<queue>
#include<ctime>
#include<vector>
#include<set>
#include<map>
#include<stack>
using namespace std;
#define pi acos(-1.0)
#define ri register int
int n,m,r[2100000],len;
struct node {
      double x,y;
      node(){};
      node(double a,double b){
         x=a,y=b;
      }
}a[2100000],b[2100000];
inline int read(){
      int x=0,f=1;char s=getchar();
      while(s<'0'||s>'9'){if(s=='-')f=-1;s=getchar();}
      while(s>='0'&&s<='9'){x=(x<<3)+(x<<1)+(s-'0');s=getchar();}
      return x*f;
}
inline node operator + (const node a,const node b){
      return node(a.x+b.x,a.y+b.y);
}
inline node operator - (const node a,const node b){
      return node(a.x-b.x,a.y-b.y);
}
inline node operator * (const node a,const node b){
      return node(a.x*b.x-a.y*b.y,a.y*b.x+a.x*b.y);
}
inline void fft(node *a,int f){
      for(ri i=0;i<n;i++)
         if(i<r[i])
           swap(a[i],a[r[i]]);
      for(ri k=1;k<n;k<<=1){
           node wn(cos(pi/k),f*sin(pi/k));
           for(ri i=0;i<n;i+=(k<<1)){
               node w(1,0),p,q;
               for(ri j=0;j<k;j++,w=w*wn){
                  p=a[i+j],q=a[i+j+k]*w;
                  a[i+j]=p+q,a[i+j+k]=p-q;
              }
           }
      }
      if(f==-1)
        for(ri i=0;i<n;i++)
           a[i].x=a[i].x/n;
}
int main()
{     n=read(),m=read();
      for(ri i=0;i<=n;i++)a[i].x=read();
      for(ri i=0;i<=m;i++)b[i].x=read();
      m+=n;
      for(n=1;n<=m;n<<=1)len++;
      for(ri i=0;i<n;i++)r[i]=((r[i>>1]>>1)|(i&1)<<(len-1));
      fft(a,1),fft(b,1);
      for(ri i=0;i<n;i++)a[i]=a[i]*b[i];
      fft(a,-1);
      for(ri i=0;i<=m;i++)printf("%d ",(int)(a[i].x+0.5));
      return 0;
}