Cod sursa(job #3266168)

Utilizator nistor_dora_valentinaNistor Dora Valentina nistor_dora_valentina Data 6 ianuarie 2025 11:42:40
Problema Pairs Scor 100
Compilator cpp-64 Status done
Runda Arhiva de probleme Marime 1.48 kb
#include <fstream>
#include <bits/stdc++.h>

using namespace std;
ifstream fin("pairs.in");
ofstream fout("pairs.out");
int t, n, i, j, divi[1000005], maxim, x, fr[1000005], c[1000005];
long long ans;
int main()
{
    fin>>n;
    for(i=1; i<=n; i++)
    {
        fin>>x;
        fr[x]++;
        maxim=max(maxim, x);
        int d=2;
        vector <int> prim;
        while(x>1)
        {
            if(x%d==0)
            {
                prim.push_back(d);
                while(x%d==0)
                    x/=d;
            }
            d++;
            if(d*d>x && x>1)
                d=x;
        }
        int k=prim.size();
        for(int mask=1; mask<(1<<k); mask++)
        {
            int pr=1, nr=0;
            for(int j=0; j<k; j++)
                if(mask&(1<<j))
            {
                nr++;
                pr*=prim[j];
            }
            if(pr<=1e6)
            {
                if(nr%2)
                 c[pr]=1;
                else
                if(nr!=0)
                 c[pr]=2;
            }
        }
    }
    for(i=2; i<=maxim; i++)
    {
        x=i;
        int p=1;
        while(x*p<=1e6)
        {
            divi[x]+=fr[x*p];
            p++;
        }
    }
    for(i=2; i<=maxim; i++)
    {
        if(c[i]==1)
          ans+=1ll*divi[i]*(divi[i]-1)/2;
        else
            if(c[i]==2)
            ans-=1ll*divi[i]*(divi[i]-1)/2;
    }
    fout<<1ll*n*(n-1)/2-ans;
    return 0;
}