[51Nod1028]大数乘法 V2
换了一种模板。。。
1 #include <iostream> 2 #include <algorithm> 3 #include <cstdio> 4 #include <cstring> 5 #include <cstdlib> 6 #include <complex> 7 using namespace std; 8 const int N=200000; 9 10 typedef complex<double> c; 11 12 char a[N],b[N]; 13 14 int rev(int x,int n){ 15 int ret=0; 16 for(int i=0;(1<<i)<n;i++)ret=(ret<<1)|((x&(1<<i))>0); 17 return ret; 18 } 19 20 21 c F[N*2]; 22 void fft(c *a,int n,int f){ 23 for(int i=0;i<n;i++)F[rev(i,n)]=a[i]; 24 for(int i=2;i<=n;i<<=1){ 25 c wn=c(cos(f*2*acos(-1)/i),sin(f*2*acos(-1)/i)); 26 for(int j=0;j<n;j+=i){ 27 c w=c(1,0); 28 for(int k=j;k<j+i/2;k++){ 29 c u=F[k]; 30 c t=w*F[k+i/2]; 31 F[k]=u+t; 32 F[k+i/2]=u-t; 33 w*=wn; 34 } 35 } 36 } 37 if(f==-1)for(int i=0;i<n;i++)F[i]/=n; 38 for(int i=0;i<n;i++)a[i]=F[i]; 39 } 40 41 42 c A[N*2],B[N*2]; 43 int ans[N*2]; 44 int main(){ 45 scanf("%s%s",a,b); 46 int len1=strlen(a),len2=strlen(b),n1=0,n2=0,n; 47 while((1 << n1) < len1)n1++; 48 while((1 << n2) < len2)n2++; 49 n = 1 << (max(n1, n2) + 1); 50 for(int i = 0; i < n; i++) 51 { 52 if(i < len1) A[i] = c(a[len1 - i - 1] - '0', 0); 53 else A[i] = c(0, 0); 54 if(i < len2) B[i] = c(b[len2 - i - 1] - '0', 0); 55 else B[i] = c(0, 0); 56 } 57 fft(A, n, 1); 58 fft(B, n, 1); 59 for(int i = 0; i < n; i++)A[i]*=B[i]; 60 fft(A, n, -1); 61 for(int i = 0; i < n; i++)ans[i] = (int)(A[i].real() + 0.5); 62 for(int i = 0; i < n - 1; i++)ans[i+1] += ans[i] / 10,ans[i] %= 10; 63 bool flag = 0; 64 for(int i = n - 1; i >= 0; i--) 65 { 66 if(ans[i]) printf("%d", ans[i]), flag = 1; 67 else if(flag || i == 0) printf("0"); 68 } 69 }
