HDU2136:Largest prime factor

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 <stdio.h>
#include <string.h>

const int N = 1000000;
int hash[N+5];
int prime[N+5];

void sushu()
{
    int  i,j;
    memset(prime,0,sizeof(prime));
    hash[1] = 0;
    int flag = 0;
    for(i = 2; i<=N; i++)
    {
        if(!prime[i])
        {
            hash[i] = ++flag;
            for(j = i; j<=N; j+=i)
            {
                prime[j] = i;
            }
        }
    }
}

int main()
{
    int i;
    memset(hash,0,sizeof(hash));
    sushu();
    while(~scanf("%d",&i))
    {
        if(i == 1)
        printf("0\n");
        else
        {
            int k = prime[i];
            printf("%d\n",hash[k]);
        }
    }

    return 0;
}