Cod sursa(job #1417366)
Utilizator | Filipescu Radu Radu_Filipescu | Data | 10 aprilie 2015 11:20:26 |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 100 |
Compilator | cpp | Status | done |
Runda | Arhiva educationala | Marime | 0.46 kb |
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
char prim[2000001];
int main()
{
unsigned int n,i,j,nr=0;
fin>>n;
fin.close();
for(i=1; i<=n; i++) prim[i]='0';
prim[2]='1';
for(i=3; i<=n; i=i+2) prim[i]='1';
for(i=3; i*i<=n; i=i+2)
for(j=3*i; j<=n; j=j+2*i) prim[j]='0';
for(i=2; i<=n; i++) if(prim[i]=='1') nr++;
fout<<nr;
fout.close();
return 0;
}