HDU 2136 Largest prime factor（素数筛选+打表）

Largest prime factor

Time Limit: 5000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 9962    Accepted Submission(s): 3514

Problem Description

Everybody knows any number can be combined by the prime number.
Now, your task is telling me what position of the largest prime factor.
The position of prime 2 is 1, prime 3 is 2, and prime 5 is 3, etc.
Specially, LPF(1) = 0.

Input

Each line will contain one integer n(0 < n < 1000000).

Output

Output the LPF(n).

Sample Input

1
2
3
4
5

Sample Output

0
1
2
1
3

Author

Wiskey

Source

AC代码：

#include<iostream>  
#include<memory.h>  
#include<cstdlib>  
#include<cstdio>  
#include<cmath>  
#include<cstring>  
#include<string>  
#include<cstdlib>  
#include<iomanip>  
#include<vector>  
#include<list>  
#include<map>  
#include<algorithm>  
typedef long long LL;  
using namespace std; 
const LL maxn=1e6;
const LL mod=10000000; 
int a[maxn]={0};
//素数筛选：打表 
int main()
{
    
    int n,k=1;
    for(int i=2;i<maxn;i++)
    {
        if(a[i]==0)
        {
            a[i]=k++; //position 
            for(int j=i+i;j<maxn;j+=i)
            {
                a[j]=a[i]; 
            }
        }
    }
    while(~scanf("%d",&n))
    {
        if(n==1)printf("0\n"); 
        else
        cout<<a[n]<<endl;
    }
    return 0;    
}