FWT

Posted 2020-09-04 G . H . O . S . T . R . E . A

FWT模板：

 1 void FWT(int a[],int n) 
 2 { 
 3     for(int d=1;d<n;d<<=1) //你甚至可以RANDOMSHUFFLE
 4     for(int m=d<<1,i=0;i<n;i+=m) 
 5     for(int j=0;j<d;j++) 
 6     { 
 7         int x=a[i+j],y=a[i+j+d]; 
 8         a[i+j]=(x+y)%mod,a[i+j+d]=(x-y+mod)%mod; 
 9         //xor:a[i+j]=x+y,a[i+j+d]=x-y;
10         //and:a[i+j]=x+y; 
11         //or:a[i+j+d]=x+y; 
12     } 
13 } 
14 
15 void UFWT(int a[],int n) 
16 {
17     for(int d=1;d<n;d<<=1) //你甚至可以RANDOMSHUFFLE
18     for(int m=d<<1,i=0;i<n;i+=m) 
19     for(int j=0;j<d;j++) 
20     { 
21         int x=a[i+j],y=a[i+j+d]; 
22         a[i+j]=1LL*(x+y)*rev%mod,a[i+j+d]=(1LL*(x-y)*rev%mod+mod)%mod; 
23         //xor:a[i+j]=(x+y)/2,a[i+j+d]=(x-y)/2; 
24         //and:a[i+j]=x-y; 
25         //or:a[i+j+d]=y-x; 
26     } 
27 } 
28 void solve(int a[],int b[],int n) 
29 { 
30     FWT(a,n); 
31     FWT(b,n); 
32     for(int i=0;i<n;i++) a[i]=1LL*a[i]*b[i]%mod; 
33     UFWT(a,n); 
34 }

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