Largest prime factor

Time Limit: 5000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)

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

原题链接:http://acm.hdu.edu.cn/showproblem.php?pid=2136

题意:求最大素因子的序号,素数序号即为在素数表中的位置,例如:第1个为 2 ,第2个为 3 ,第 3 个为 5,

特别规定:第 0 个为 1.

用了素数筛选法还是超时,网上查看别人的代码,几乎一模一样,最后发现,别人用的是scanf(),printf(),而我用的是cin,cout,一改,便A了.

AC代码:

#include <iostream>
#include <cstdio>
using namespace std;
#define maxn 1000000+5
int a[maxn];
int main()
{
    int ans=0;
    for(int i=2;i<maxn;i++)
    {
        if(!a[i])
        {
            ans++;
            for(int j=i;j<maxn;j+=i)
                a[j]=ans;
        }
    }
    int n;
    while(scanf("%d",&n)!=EOF)
    {
        printf("%d\n",a[n]);
    }
    return 0;
}