poj1411

简单题

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

#define maxn 100005

bool is[maxn];
long long prm[maxn];
int n, a, b, m, p, q;

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 binarysearch()
{
    int l = 0;
    int r = n;
    while (l < r)
    {
        int mid = (l + r) / 2 + ((l + r) & 1);
        if (((long long)prm[mid]) * prm[mid] <= m)
            l = mid;
        else
            r = mid - 1;
    }
    return l;
}

void work(int l, int r)
{
    int ans = prm[l] * prm[r];
    q = p = prm[l];
    while (l >= 0)
    {
        if (prm[l] * b < a * prm[r])
            break;
        while (r < n - 1 && prm[l] * b >= a * prm[r + 1] && prm[l] * prm[r + 1] <= m)
            r++;
        if (ans < prm[l] * prm[r])
        {
            p = prm[l];
            q = prm[r];
            ans = prm[l] * prm[r];
        }
        l--;
    }
    printf("%d %d\n", p, q);
}

int main()
{
    //freopen("t.txt", "r", stdin);
    n = getprm(maxn - 1);
    while (scanf("%d%d%d", &m, &a, &b), m | a | b)
    {
        int l, r;
        l = r = binarysearch();
        work(l, r);
    }
    return 0;
}