COGS 1473 O(N*logN) 高精乘 FFT

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题意: 求A*B, A <= 10^150000

万进制亿进制走吧,放弃吧...

正解fft 模板么,随便搞搞就好了...

#include <iostream>#include <cstring>#include <algorithm>#include <stdio.h>#include <math.h>using std::swap;#define MAXN 530010const double PI = acos(-1.0);char s1[MAXN],s2[MAXN];int rev[MAXN],N,len,len1,len2,cnt,Ans[MAXN];    template<typename _t>inline _t read(){    _t x=0,f=1;    char ch=getchar();    for(;ch>'9'||ch<'0';ch=getchar())if(ch=='-')f=-f;    for(;ch>='0'&&ch<='9';ch=getchar())x=x*10+(ch^48);    return x*f;}  struct Complex{    double x,y;    inline Complex operator + (const Complex & a){return (Complex){x+a.x,y+a.y};}    inline Complex operator - (const Complex & a){return (Complex){x-a.x,y-a.y};}    inline Complex operator * (const Complex & a){return (Complex){x*a.x-y*a.y,x*a.y+y*a.x};}}a[MAXN],b[MAXN],c[MAXN];  inline void fft(Complex *a,int type){    Complex wn,w,t;    for(int i=0;i<N;i++)if(i<rev[i])swap(a[i],a[rev[i]]);    for(int k=2;k<=N;k<<=1){        wn = (Complex){cos(type*2*PI/k),sin(type*PI*2/k)};        for(int j=0;j<N;j+=k){            w = (Complex){1,0};            for(int i=0;i<(k>>1);i++,w=w*wn)                t=a[i+j+(k>>1)]*w,a[i+j+(k>>1)]=a[i+j]-t,a[i+j]=a[i+j]+t;        }    }    if(type==-1) for(int i=0;i<N;i++) a[i].x/=N;}  void FFT(Complex *a,Complex *b,int *Ans,int tot){    for(N=1;N<(tot<<1);len++,N<<=1);    for(int i=0;i<N;i++) {        if(i&1)rev[i]=(rev[i>>1]>>1)|(N>>1);        else rev[i]=rev[i>>1]>>1;    }    fft(a,1);fft(b,1);    for(int i=0;i<N;i++) c[i]=a[i]*b[i];fft(c,-1);    for(int i=0;i<N;i++) Ans[i]=round(c[i].x);}  int main(){    scanf("%s%s",s1,s2);    len1=strlen(s1);len2=strlen(s2);    cnt = len1>len2?len1:len2;    for(int i=0;i<len1;i++)a[i].x=s1[len1-i-1]-48;    for(int i=0;i<len2;i++)b[i].x=s2[len2-i-1]-48;    FFT(a,b,Ans,cnt);    for(int i=0;i<N;i++) {        Ans[i+1] += Ans[i] / 10;        Ans[i] %= 10;    }    len = len1+len2;    while(!Ans[len]&&len>=1)--len;    for(int i=len;i>=0;i--)printf("%c",Ans[i]+'0');}

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