BZOJ 4259: 残缺的字符串 FFT_多项式

Code:

#include<bits/stdc++.h>     
#define maxn 1200000       
using namespace std; 
void setIO(string s)
{
    string in=s+".in", out=s+".out"; 
    freopen(in.c_str(),"r",stdin); 
    freopen(out.c_str(),"w",stdout);  
} 
#define pi 3.1415926535898
struct cpx
{
    double x,y; 
    cpx(double a=0,double b=0){x=a,y=b;} 
    cpx operator+(const cpx b){ return cpx(x+b.x,y+b.y); }
    cpx operator-(const cpx b){ return cpx(x-b.x,y-b.y); }
    cpx operator*(const cpx b){ return cpx(x*b.x-y*b.y,x*b.y+y*b.x); }   
}a1[maxn],a2[maxn],a3[maxn],b1[maxn],b2[maxn],b3[maxn]; 
void FFT(cpx *a,int n,int flag)
{   
    for(int i=0,k=0;i<n;++i)
    {
        if(i>k) swap(a[i],a[k]); 
        for(int j=n>>1;(k^=j)<j;j>>=1); 
    }
    for(int mid=1;mid<n;mid<<=1)
    {
        cpx wn(cos(pi/mid), flag*sin(pi/mid)),x,y; 
        for(int j=0;j<n;j+=(mid<<1))
        {
            cpx w(1,0);  
            for(int k=0;k<mid;++k) 
            {
                x=a[j+k],y=w*a[j+mid+k];          
                a[j+k]=x+y, a[j+k+mid]=x-y; 
                w=w*wn;     
            }
        }
    }                      
} 
char str1[maxn],str2[maxn];  
int n,m,len=1; 
int arr[maxn],brr[maxn];   
queue<int>Q; 
int main()
{
    // setIO("input");  
    scanf("%d%d%s%s",&n,&m,str1,str2);    
    while(len<n+m)len<<=1;  
    for(int i=0;i<n;++i) arr[n-1-i]=str1[i]=='*'?0.00:(double)str1[i]-'a'+1;   
    for(int i=0;i<m;++i) brr[i]=str2[i]=='*'?0.00:(double)str2[i]-'a'+1; 
    for(int i=0;i<n;++i) a1[i]=cpx(arr[i]*arr[i]*arr[i],0),a2[i]=cpx(arr[i],0), a3[i]=cpx(arr[i]*arr[i],0); 
    for(int i=0;i<m;++i) b1[i]=cpx(brr[i],0), b2[i]=cpx(brr[i]*brr[i]*brr[i],0), b3[i]=cpx(brr[i]*brr[i],0); 
    FFT(a1,len,1),FFT(a2,len,1),FFT(a3,len,1),FFT(b1,len,1),FFT(b2,len,1),FFT(b3,len,1); 
    for(int i=0;i<len;++i) a1[i]=a1[i]*b1[i]+a2[i]*b2[i]-a3[i]*b3[i]-a3[i]*b3[i]; 
    FFT(a1,len,-1);              

    for(int i=0;i+n-1<m;++i) if((int)(a1[i+n-1].x/len+0.1)==0) Q.push(i+1); 
    printf("%d\n",Q.size());
    while(!Q.empty())
    {
        printf("%d ",Q.front()); 
        Q.pop(); 
    }
    return 0; 
}