UVA1521/Gym-100085G GCD Guessing Game 思维+素数筛选

这道题至今很迷。。。就是emmmm感性的感觉一下？？

附上参考博客Orz：https://blog.csdn.net/commonc/article/details/51790027

                               https://www.cnblogs.com/oldmanren/archive/2012/11/23/2784986.html

附上AC代码：

#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<iostream>
#include<algorithm>
using namespace std;
#define ll long long
typedef pair<int,int>pp;
const double pi=acos(-1.0);
const double eps=1e-9;
const int INF=0x3f3f3f3f;
const ll MOD=1e9+7ll;

const int MAX=10005;
int n;
int p[MAX],cnt;
bool prime[MAX];
void getp(int n)
{
    memset(prime,false,sizeof(prime));
    cnt=0;
	int i,j;
	for(i=2;i<=n;i++)
	{
		if(!prime[i])
            cnt++,p[cnt]=i;
		for(j=1;j<=cnt&&i*p[j]<=n;j++)
		{
			prime[i*p[j]]=true;
			if(i%p[j]==0)
                break;
		}
	}
}
int main()
{
    freopen("gcd.in","r",stdin);
    freopen("gcd.out","w",stdout);
    int n;
    while(scanf("%d",&n)==1)
    {
        getp(n);
        int i=1,j=cnt;
        int ans=0;
        while(i<=j)
        {
            ans++;
            if(p[i]*p[j]<=n)
                i++,j--;
            else
                j--;
        }
        printf("%d\n",ans);
    }
}