poj2262

简单题

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
using namespace std;

#define N 1000005

bool is[N];
int prm[N];

int getprm(int n)
{
    int i, j, k = 0;
    int s, e = (int )(sqrt(0.0+n) +1);
    memset(is, 1, sizeof(is));
    prm[k++] = 2; is[0] = is[1] = 0;
    for (i =4; i < n; i+= 2) is[i] = 0;
    for(i = 3; i < e; i+=2)
        if (is[i])
        {
            prm[k++] = i;
            for(s = i * 2, j = i * i; j < n; j+=s)
                is[j] = 0;
        }
    for(; i < n; i+=2)
        if (is[i])prm[k++] = i;
    return k;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    int tot = getprm(1000000);
    int n;
    while (scanf("%d", &n), n)
    {
        for (int i = 0; i < tot && prm[i] * 2 <= n; i++)
            if (is[n - prm[i]])
            {
                printf("%d = %d + %d\n", n, prm[i], n - prm[i]);
                break;
            }
    }
    return 0;
}