HDU 2136 Largest prime factor 数论

Largest prime factor

Time Limit:1000MS     Memory Limit:32768KB     64bit IO Format:%I64d & %I64u

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

还是预处理

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <queue>
#include <vector>
#include <iomanip>
#include <math.h>
using namespace std;
#define FIN     freopen("input.txt","r",stdin);
#define INF     0x3f3f3f3f
#define lson    l,m,rt<<1
#define rson    m+1,r,rt<<1|1
typedef long long LL;

int p[1000005];

int main()
{
    //FIN
    int cou=0;
    for(int i=2; i<=1000000; i++)
    {
        if(p[i]==0)
        {
            cou++;
            for(int j=i; j<=1000000; j=j+i)
            {
                p[j]=cou;
            }
        }
    }

    int n;
    while(~scanf("%d",&n))
    {
        printf("%d\n",p[n]);
    }

}