洛谷 P1919 【模板】A*B Problem升级版（FFT快速傅里叶）

吐槽下P3803都是紫题...
真心好写，本想一遍过的...但是
我真是太菜了...
 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 const int MAXN=200000;
 4 const double pi=acos(-1.0);
 5 char x[MAXN],y[MAXN];
 6 int sum,lena,lenb,l;
 7 int TT[MAXN],c[MAXN];
 8 int r;
 9 int n,m;
10 struct Node{
11     //int x;
12     double x;
13     double y;
14     Node (double x1=0,double y1=0){
15         x=x1,y=y1;
16     }
17 }a[MAXN],b[MAXN];
18 Node operator * (Node x,Node y){
19     return Node(x.x*y.x-x.y*y.y,x.x*y.y+x.y*y.x);
20 }
21 Node operator + (Node x,Node y){
22     return Node(x.x+y.x,x.y+y.y);
23 }
24 Node operator - (Node x,Node y){
25     return Node(x.x-y.x,x.y-y.y);
26 }
27 inline void fft(Node *g,double tf){
28     for (int i=0;i<sum;++i)
29         if (i<c[i])
30             swap(g[i],g[c[i]]);
31     for (int j=1;j<sum;j<<=1){
32         Node T(cos(pi/j),tf*sin(pi/j));
33         for (int k=0;k<sum;k+=(j<<1)){
34             Node T1(1,0);
35             for (int l=0;l<j;l++,T1=T*T1){
36                 Node x1=g[k+l];
37                 Node y1=T1*g[k+j+l];
38                 g[k+l]=x1+y1;
39                 g[k+j+l]=x1-y1;
40             }
41         }
42     }
43 }
44 int main(){
45     scanf("%d",&n);
46     scanf("%s%s",x,y);
47     //printf("%s",x);
48     for (int i=n-1;i>=0;i--){
49         a[lena++].x=x[i]-48;
50         b[lenb++].x=y[i]-48;
51     }
52     sum=1;
53     while (sum<n+n) sum<<=1,l++;
54     for (int i=0;i<=sum;++i)
55         c[i]=(c[i>>1]>>1)|((i&1)<<(l-1));
56     fft(a,1),fft(b,1);
57     for (int i=0;i<=sum;++i)
58         a[i]=a[i]*b[i];
59     fft(a,-1);
60     for (int i=0;i<=sum;++i){
61         TT[i]+=(int) (a[i].x/sum+0.5);
62         if (TT[i]>=10){
63             TT[i+1]+=TT[i]/10;
64             TT[i]%=10;
65             if (i==sum)
66                 sum++;
67         }
68     }
69     while (!TT[sum] && sum>=1)
70         sum--;
71     sum++;
72     while (--sum>=0)
73         printf("%d",TT[sum]);
74     return 0;
75 }