Thursday, November 3, 2016

UVA 10948 - The primary problem

#include<bits/stdc++.h>
#define sf scanf
#define pf printf
#define LL long long
#define REP(i,MAX) for(int i = 0; i<MAX; i++)
#define MAX 1000010
bool prime[MAX];
using namespace std;
void init_prime() {
  prime[2] = true;
  for (int i = 3; i < MAX; i += 2) prime[i] = true;

  for (int i = 3; i*i < MAX; i += 2)
    if (prime[i])
      for (int j = i*i; j < MAX; j += i+i)
        prime[j] = false;
}

int main()
{
    ios_base::sync_with_stdio(false);
    init_prime();
    int n;
    while(cin >> n && n){
        cout << n << ":\n";
        bool found = false;
        int i;
        for (i = 2; i <= n; ++i)
        {
            if(i > n-i)break;
            if(prime[i] && prime[n-i]){
                found = true;
                break;
            }
        }
        if(found)cout <<i<<'+'<<n-i<<'\n';
        else cout <<"NO WAY!\n";
    }


 return 0;
}

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