Question

sa se scrie un program care va determina cate nr prime mai mici egale ca n sunt? repede va rog dau coroana

Answer 1

#include <iostream>

using namespace std;

int n, num, nrprime;

bool prim(int m)

{

   int p=1;

   for (int j=3; j*j<=m; j+=2)

   {

       if (m%j==0) {p=0; break;}

   }

   return p==1;

}

int main()

{

   cout << "n= "; cin >> n;

   if (n<2) nrprime=0;

   if (n==2) nrprime=1;

   if (n>2)

   {

       nrprime=1;

       for (num=3; num<=n; num+=2)

       {

           if (prim(num)) ++nrprime;

       }

   }

   cout << nrprime;

}

Answer 2

#include<bits/stdc++.h>

using namespace std;

typedef long long ll;

ll const mod=1000000007;

ll const md=998244353;

ll mypowr(ll a,ll b) {ll res=1;a%=mod; assert(b>=0);

for(;b;b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;}

ll mypow(ll a,ll b) {ll res=1;assert(b>=0);

for(;b;b>>=1){if(b&1)res=res*a;a=a*a;}return res;}

ifstream in("elevi.in");

ofstream out("elevi.out");

#define mp make_pair

#define pb push_back

#define pf push_front

#define fi first

#define se second

int p(ll x){

if(x<=1)return 0;

if(x<=3)return 1;

if(x%2==0||x%3==0)return 0;

for(ll i=5;i*i<=x;i+=6){

   if(x%i==0||x%(i+2)==0)return 0;

}

return 1;

}

int main()

{

   ios_base::sync_with_stdio(0);

   cout<<fixed<<setprecision(15);

   cin.tie(0);cout.tie(0);

   ll n,cnt=0;

   cin>>n;

   if(n>1)++cnt;

   for(int i=3;i<=n;i+=2){

       cnt+=p(i);

   }

   cout<<cnt<<'\n';

   return 0;

}