HDU : 2161 (Primes)


// http://acm.hdu.edu.cn/showproblem.php?pid=2161

// @BEGIN_OF_SOURCE_CODE

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <string>
#include <cctype>
#include <stack>
#include <queue>
#include <list>
#include <vector>
#include <map>
#include <sstream>
#include <utility>
#include <set>
#include <math.h>
#define pi acos(-1.0)
#define N 1000000
using namespace std;

bool mark [N];

void sieve ()
{
    memset (mark, true, sizeof (mark));

    mark [0] = mark [1] = false;

    for ( int i = 4; i < N; i += 2 )
        mark [i] = false;

    for ( int i = 3; i * i <= N; i += 2 ) {
        if ( mark [i] ) {
            for ( int j = i * i; j < N; j += 2 * i )
                mark [j] = false;
        }
    }
}

int main ()
{
    sieve ();

    mark [2] = false;

    int n;
    int cases = 0;

    while ( scanf ("%d", &n) ) {
        if ( n <= 0 )
            break;

        if ( mark [n] )
            printf ("%d: yes\n", ++cases);
        else
            printf ("%d: no\n", ++cases);
    }

    return 0;
}

// @END_OF_SOURCE_CODE
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