HDU 2136 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
题意：最大因子的位置。思路见AC代码：
#include<stdio.h>
#include<math.h>
#define N 1000010
int prime[N];
int main()
{
    int s,i,n,j,k,num;
    prime[1]=0;
    num=0;
    for(i=2; i<N; i++) 
    {
    //因为2和3都是素数，所以2的倍数，3的倍数就会更新
    //4是2的倍数，perim[4]还是1...
        if(prime[i]==0) 
        {
            num++;    //遇到一个素数，顺序加一个...表明第几个素数因子
            for(j=i; j<N; j=j+i)    //更新 新出现素数的所有倍数...此时被更新的值就是此时最大的因子
                prime[j]=num;
        }
    }
    while(scanf("%d",&n)!=EOF)
    {
        printf("%d\n",prime[n]);//只需输出，在上述步骤得到的prime[n]即可，
    }
    return 0;
}