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

通過素數篩的過程中來求得最大素數因子。。。

程式碼如下：

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <math.h>
#include <vector>
using namespace std;
const int maxn=1000010;
int Isn[maxn];
int n;
vector<int>ve;
int loc[maxn];
void init()
{
    memset (Isn,0,sizeof(Isn));
}
void Is_prime()
{
    loc[1]=0;
    for (int i=2,k=1;i<maxn;i++)
    {
          if(!Isn[i])
          {
              loc[i]=k++;
              for (int j=i;j<maxn;j+=i)
              {
                        Isn[j]=i;
              }
          }
    }
}
int main()
{
    init();
    Is_prime();
    while (scanf("%d",&n)!=EOF)
    {
        printf("%d\n",loc[Isn[n]]);
    }
    return 0;
}