POJ 2429 GCD & LCM Inverse（Pollard_Rho+dfs）

#include <cstdio>
#include <algorithm>
#include <cmath>
#define C 2730
#define S 3
using namespace std;
typedef long long ll;
ll n,m,s[1000],cnt,f[1000],cnf,ans;
ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
ll mul(ll a,ll b,ll n){return(a*b-(ll)(a/(long double)n*b+1e-3)*n+n)%n;}
ll pow(ll a, ll b, ll n){
    ll d=1; a%=n;
    while(b){
        if(b&1)d=mul(d,a,n);
        a=mul(a,a,n);
        b>>=1;
    }return d;
}
bool check(ll a,ll n){
    ll m=n-1,x,y;int i,j=0;
    while(!(m&1))m>>=1,j++;
    x=pow(a,m,n);
    for(i=1;i<=j;x=y,i++){
        y=pow(x,2,n);
        if((y==1)&&(x!=1)&&(x!=n-1))return 1;
    }return y!=1;
}
bool miller_rabin(int times,ll n){
    ll a;
    if(n==1)return 0;
    if(n==2)return 1;
    if(!(n&1))return 0;
    while(times--)if(check(rand()%(n-1)+1,n))return 0;
    return 1;
}
ll pollard_rho(ll n,int c){
    ll i=1,k=2,x=rand()%n,y=x,d;
    while(1){
        i++,x=(mul(x,x,n)+c)%n,d=gcd(y-x,n);
        if(d>1&&d<n)return d;
        if(y==x)return n;
        if(i==k)y=x,k<<=1;
    }
}
void findfac(ll n,int c){
    if(n==1)return;
    if(miller_rabin(S,n)){
        s[cnt++]=n;
        return;
    }ll m=n;
    while(m==n)m=pollard_rho(n,c--);
    findfac(m,c),findfac(n/m,c);
}
void dfs(int pos,long long x,long long k){  
    if(pos>cnf)return;  
    if(x>ans&&x<=k)ans=x;  
    dfs(pos+1,x,k);  
    x*=f[pos];  
    if(x>ans&&x<=k)ans=x;  
    dfs(pos+1,x,k);  
} 
int main(){
    while(~scanf("%lld%lld",&m,&n)){
        if(n==m){printf("%lld %lld\n",n,n);continue;}
        cnt=0; long long k=n/m;
        findfac(k,C);
        sort(s,s+cnt);
        f[0]=s[0]; cnf=0;
        for(int i=1;i<cnt;i++){
            if(s[i]==s[i-1])f[cnf]*=s[i];
            else f[++cnf]=s[i];
        }long long tmp=(long long)sqrt(1.0*k);
        ans=1; dfs(0,1,tmp);
        printf("%lld %lld\n",m*ans,k/ans*m);
    }return 0;
}