题目链接:http://oj.xjtuacm.com/problem/13/
题目大意:$T$组数据,每组给出$n$个数$a_i$及一个素数$m$,求这$n$个数两两相乘模$m$余$k$有多少个($0\leqslant k < m$).
数论+FFT
原根的概念
设$n \geqslant 1$,$(a,n)=1$,使得$a^d \equiv 1(mod n)$成立的最小的正整数$d$,被称为$a$对模$n$的阶,记做$\delta_n(a)$.
当$\delta_n(a)=\varphi(n)$时,称$a$为模$n$的一个原根.
待更...
代码如下:
1 #include <cstdio> 2 #include <cmath> 3 #include <iostream> 4 #include <cstring> 5 #define N 60010 6 using namespace std; 7 typedef long long ll; 8 ll T,n,m,t,r,len,phi; 9 ll ans[N],mod[N],rt[N],temp[4*N]; 10 const double pi=acos(-1.0); 11 struct Complex{ 12 double r,i; 13 Complex(double r=0,double i=0):r(r),i(i){}; 14 Complex operator+(const Complex &rhs){return Complex(r+rhs.r,i+rhs.i);} 15 Complex operator-(const Complex &rhs){return Complex(r-rhs.r,i-rhs.i);} 16 Complex operator*(const Complex &rhs){return Complex(r*rhs.r-i*rhs.i,i*rhs.r+r*rhs.i);} 17 }a[4*N],b[4*N],c[4*N]; 18 void sincos(double theta,double &p0,double &p1){ 19 p0=sin(theta);p1=cos(theta); 20 } 21 void fft_main(Complex P[], ll n, ll oper){ 22 for(ll i=1,j=0;i<n-1;i++){ 23 for(ll s=n;j^=s>>=1,~j&s;); 24 if(i<j)swap(P[i],P[j]); 25 } 26 Complex unit_p0; 27 for(ll d=0;(1<<d)<n;d++){ 28 ll m=1<<d,m2=m*2; 29 double p0=pi/m*oper; 30 sincos(p0,unit_p0.i,unit_p0.r); 31 for(ll i=0;i<n;i+=m2){ 32 Complex unit=1; 33 for(ll j=0;j<m;j++){ 34 Complex &P1=P[i+j+m],&P2=P[i+j]; 35 Complex t=unit*P1; 36 P1=P2-t; P2=P2+t; 37 unit=unit*unit_p0; 38 } 39 } 40 }if(oper==-1)for(ll i=0;i<len;i++)P[i].r/=len; 41 } 42 void fft(Complex a[],Complex b[],ll len){ 43 fft_main(a,len,1);fft_main(b,len,1); 44 for(ll i=0;i<len;++i)c[i]=a[i]*b[i]; 45 fft_main(c,len,-1); 46 } 47 void fft_init(){ 48 len=1; 49 while(len<2*phi)len<<=1; 50 ll i=0; 51 for(ll x=1;i<phi;++i){ 52 rt[i]=mod[x]; 53 a[i].r=b[i].r=rt[i]; 54 a[i].i=b[i].i=0; 55 x=(x*r)%m; 56 } 57 for(;i<len;++i){ 58 a[i].r=b[i].r=0; 59 a[i].i=b[i].i=0; 60 } 61 } 62 ll powmod(ll a,ll n,ll m){ 63 ll r=1,t=a; 64 while(n){ 65 if(n&1)r=(r*t)%m; 66 t=(t*t)%m; 67 n>>=1; 68 } 69 return r; 70 } 71 ll Root(ll m){ 72 for(ll i=2,j;i<m;++i){ 73 for(j=2;j<phi;++j) 74 if(powmod(i,j,m)==1) 75 break; 76 if(j==phi)return i; 77 } 78 return 0; 79 } 80 ll in(){ 81 ll res=0,flag=0,ch; 82 if((ch=getchar())==‘-‘)flag=1; 83 else if(‘0‘<=ch&&ch<=‘9‘)res=ch-‘0‘; 84 while(‘0‘<=(ch=getchar())&&ch<=‘9‘)res=res*10+ch-‘0‘; 85 return flag?-res:res; 86 } 87 void out(ll x){ 88 if(x>9)out(x/10); 89 putchar(x%10+‘0‘); 90 } 91 void solve(){ 92 for(ll i=0;i<len;++i){ 93 temp[i]=c[i].r+0.5; 94 temp[i]/=2; 95 } 96 for(ll i=0;i<phi;++i){ 97 temp[2*i]-=rt[i]*rt[i]/2; 98 temp[2*i]+=rt[i]*(rt[i]-1)/2; 99 } 100 for(ll i=0,x=1;i<len;++i){ 101 ans[x]+=temp[i]; 102 x=(x*r)%m; 103 } 104 ans[0]=mod[0]*(n-mod[0])+mod[0]*(mod[0]-1)/2; 105 } 106 void init(){ 107 memset(temp,0,sizeof(temp)); 108 n=in();m=in(); 109 for(ll i=0;i<m;++i)mod[i]=0; 110 for(ll i=0;i<m;++i)ans[i]=0; 111 for(ll i=0;i<n;++i){ 112 t=in(); 113 mod[t%m]++; 114 } 115 } 116 int main(void){ 117 T=in(); 118 while(T--){ 119 init(); 120 phi=m-1; 121 r=Root(m); 122 fft_init(); 123 fft(a,b,len); 124 solve(); 125 for(ll i=0;i<m;++i){ 126 out(ans[i]); 127 puts(""); 128 } 129 } 130 }
原文:http://www.cnblogs.com/barrier/p/6697179.html