Pagini recente » Borderou de evaluare (job #2068909) | Cod sursa (job #250118) | Borderou de evaluare (job #2094306) | Borderou de evaluare (job #1012012) | Cod sursa (job #921088)
Cod sursa(job #921088)
#include <fstream>
using namespace std;
ifstream f("pairs.in");
ofstream g("pairs.out");
const int MAX_N = 100005;
const int MAX_VAL = 1000000;
int n, a[MAX_N], prime[MAX_VAL], nrprimes, NIVEL;
long long rez, val;
int X[MAX_VAL], cnt[MAX_VAL]; // X[i] = cate numere din M sunt divizibile cu i
bool frecv[MAX_VAL], prim[MAX_VAL + 5];
void ciur() {
for (int i = 2; i <= MAX_VAL; i++)
prim[i] = 1;
for (int i = 2; i * i <= MAX_VAL; i++)
if (prim[i]) {
for (int j = i * i; j <= MAX_VAL; j += i)
prim[j] = 0;
}
for (int i = 2; i <= MAX_VAL; i++)
if (prim[i])
prime[++nrprimes] = i;
}
void read() {
f >> n;
for (int i = 1; i <= n; i++) {
f >> a[i];
frecv[a[i]] = 1;
}
}
void precompute() {
for (int i = 2; i <= 15; i++) {
for (int j = i; j <= 15; j += i)
if (frecv[j])
X[i]++;
}
for (int i = 2; i <= 15; i++) {
if (prim[i])
for (int j = i; j <= 15; j += i)
cnt[j]++; // factorul prim i apare in descompunerea lui j
}
}
void solve() {
for (int i = 2; i <= MAX_VAL; i++)
if (X[i]) {
if (cnt[i] % 2 == 0)
rez -= 1LL * X[i] * (X[i] - 1) / 2;
else
rez += 1LL * X[i] * (X[i] - 1) / 2;
}
rez = 1LL * n * (n - 1) / 2 - rez;
}
int main() {
ciur();
read();
precompute();
solve();
g << rez << '\n';
f.close();
g.close();
return 0;
}