HDU 2136（数论，筛选打表）

Largest prime factor

Time Limit: 5000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 1481    Accepted Submission(s): 436

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
   
   
   
   
   
   
   
   

    
    
    #include <iostream>
#include <math.h>
using namespace std;
#define N 1000005

int a[N],cnt;
int elem[N];

bool prime(int u)
{
	if(u==0 || u==1) return false;
	if(u==2) return true;
	if(u%2==0) return false;
	int i;
	int temp=sqrt((double)u);
	for(i=3;i<=temp;i+=2)
		if(u%i==0) return false;
		return true;
}

void init()
{
	int i,j;
	a[0]=1;
	cnt=1;
	elem[1]=0;
	for(i=2;i<N;i++)
	{
		if(prime(i))
		{
			for(j=i;j<N;j+=i)
			elem[j]=cnt;
			cnt++;
		}
	}
}

int main()
{
	init();
	int n;
	while (scanf("%d",&n)!=EOF)
	{
		printf("%d/n",elem[n]);
	}
	return 0;
}