Cod sursa(job #3176995)

Utilizator RobertAcAcatrinei Robert-Marian RobertAc Data 28 noiembrie 2023 10:50:04
Problema Pairs Scor 10
Compilator cpp-64 Status done
Runda Arhiva de probleme Marime 1.24 kb
#include <bits/stdc++.h>
#ifdef LOCAL
#define in cin
#define out cout
#endif

using namespace std;

#ifndef LOCAL
ifstream in("pairs.in");
ofstream out("pairs.out");
#endif

const int valmax = 1e6+5;
const int sqmax = 1e3+5;

bool ciur[sqmax];
int morb[valmax];
int freq[valmax];

vector<int> primes;

void euler()
{
    primes.push_back(2);
    for(int i=3;i<sqmax;i+=2)
    {
        if(!ciur[i])
        {
            primes.push_back(i);
            for(int j=i*i;j<sqmax;j+=i)
            {
                ciur[j]=1;
            }
        }
    }
}

void morbius()
{
    for(int i=1;i<valmax;i++)morb[i]=1;
    for(auto i:primes)
    {
        for(int j=i;j<valmax;j+=i)morb[j]*=-1;
        for(int j=i*i;j<valmax;j+=i*i)morb[j]=0;
    }
}

void ion()
{
    for(int i=2;i<valmax;i++)
    {
        if(morb[i]==0)continue;
        for(int j=2*i;j<valmax;j+=i)
        {
            freq[i]+=freq[j];
        }
    }
}

int main()
{
    euler();
    morbius();
    int n;in>>n;
    for(int i=0;i<n;i++)
    {
        int nr;in>>nr;
        freq[nr]++;
    }
    ion();
    int ans = n*(n-1)/2;
    for(int i=2;i<valmax;i++)
    {
        ans+=morb[i]*freq[i]*(freq[i]-1)/2;
        //if(freq[i]!=0)cerr<<i<<' '<<morb[i]<<' '<<freq[i]<<'\n';
    }
    out<<ans;
}