Lilght Oj 1259 Goldbach's Conjecture Solution

 ///La ilaha illellahu muhammadur rasulullah

///******Bismillahir-Rahmanir-Rahim******///

///Abul Hasnat  Tonmoy

///Department of CSE,23rd batch

///Islamic University,Bangladesh

Solution in c++:

#include<bits/stdc++.h>

#define M 10000009

typedef long long ll;

using namespace std;

bool marked[M];

vector<ll>prime;

void sieve(ll n)

{

    for(ll i=4; i<=n; i+=2)

        marked[i]=true;

    for(ll i=3; i*i<=n; i+=2)

    {

        if(marked[i]==false)

        {

            for(ll j=i*i; j<=n; j+=i)

            {

                marked[j]=true;

            }

        }

    }

    prime.push_back(2);

    marked[2]=false;

    for(ll i=3; i<=n; i+=2)

    {

        if(marked[i]==false)

        {

            prime.push_back(i);

        }

    }

}

main()

{

    ll n,cnt,k,i,t,d;

    sieve(M);

    cin>>t;

    for(k=1; k<=t; k++)

    {

        cnt=0;

        cin>>n;

        for(i=0; prime[i]<=n/2;i++)

        {

            d=n-prime[i];

            if(marked[d]==false)

                cnt++;

        }

        printf("Case %d: %d\n",k,cnt);

    }

}