2136 Largest prime factor（打表）

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

题意：就是求最大素因子的在素数表中的位置.

 1 #include <stdio.h>
 2 #include <math.h>
 3 #include <queue>
 4 #include <vector>
 5 #include <stack>
 6 #include <map>
 7 #include <string>
 8 #include <cstring>
 9 #include <algorithm>
10 #include <iostream>
11 using namespace std;
12 #define N 1000000
13 int a[N];
14 void pd(){
15     int n=0,i,t,j;
16     memset(a,0,sizeof(a));
17     for(i=2;i<=N;i++)//对当前数的每个数的倍数进行赋值素数编号 可以覆盖哦 因为要覆盖为最大因子
18     {
19         if(a[i]==0)
20         {
21             n++;//素数i的位置
22             for(j=i;j<=N;j+=i)//构造出j的暂时最大素数因子的位置
23                 a[j]=n;
24         }
25     }
26 }
27 int main()
28 {
29     int i;
30     pd();
31     while(~scanf("%d",&i))
32     {
33         printf("%d\n",a[i]);
34     }
35     return 0;
36 }