Cod sursa(job #2567779)
Utilizator | Brasoveanu Mircea denmircea | Data | 3 martie 2020 18:50:59 |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 10 |
Compilator | cpp-64 | Status | done |
Runda | Arhiva educationala | Marime | 0.55 kb |
#include <bits/stdc++.h>
#define dim 1000005
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bitset<dim> fr;
int n,i,nr,j;
int main(){
fin>>n;
/// de la 2*i+1 adica 3 adaug cate 2
/// vorbim despre 3(2*i+1)
/// 6i + 3
/// 2*(3i+1) + 1
/// adaug 2(2*i+1)
if(n==2){
cout<<1;
return 0;
}
if(n%2==0)
n--;
n/=2;
for(i=1;i<=n;i++){
if(fr[i]==0){
nr++;
for(j=3*i+1;j<=n;j+=4*i){
fr[j]=1;
}
}
}
fout<<nr+1;
}