HDU 2136 Largest prime factor 数论

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <queue>
#include <vector>
#include <iomanip>
#include <math.h>
using namespace std;
#define FIN     freopen("input.txt","r",stdin);
#define INF     0x3f3f3f3f
#define lson    l,m,rt<<1
#define rson    m+1,r,rt<<1|1
typedef long long LL;

int p[1000005];

int main()
{
    //FIN
    int cou=0;
    for(int i=2; i<=1000000; i++)
    {
        if(p[i]==0)
        {
            cou++;
            for(int j=i; j<=1000000; j=j+i)
            {
                p[j]=cou;
            }
        }
    }

    int n;
    while(~scanf("%d",&n))
    {
        printf("%d\n",p[n]);
    }

}