Largest prime factor

Total Submission(s): 7169 Accepted Submission(s): 2175

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 HDU 2007-11 Programming Contest_WarmUp

学到了，一直t，直到改成i*j<Max用来当做判定条件才过

#include<bits/stdc++.h> 
using namespace std;
typedef long long ll;
#define INF 0x3f3f3f3f
#define Max int(1e6+10)
int b[Max];
bool is(int x)
{
	for(int i=2;i<=sqrt(x);i++)
	  if(x%i==0)
	    return 0;
	return 1;    
}
int main()
{
	int n,i,j,k=0;
    for(i=1;i<Max;i++)
        {
        	if(is(i))
        	{
        		for(j=1;i*j<Max;j++)
        		       	b[j*i]=k;
					   k++;
			}
			
		}
		
    while(~scanf("%d",&n)) 
	{
		 printf("%d\n",b[n]); 
	}
		
	
  return 0;	
}