HDU2136

Largest prime factor

Time Limit: 5000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 1624    Accepted Submission(s): 499

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

12345

 

 

Sample Output

01213
题目大意：
每个素数在素数表中都有一个序号，设1的序号为0，则2的序号为1，3的序号为2，5的序号为3，以此类推。现在要求输出所给定的数n的最大质因子的序号，0<n<1000000
ac代码：
#include<cstdio>#include<cstring>#include<cmath>#include<iostream>#define N 1000005using namespace std;int a[N];int main(){    int k=0, n;    memset(a, 0, sizeof(a));    for(int i=2; i<N; i++)    {        if(!a[i]){                k++;            for(int j =i; j<N; j+=i)                a[j] = k;        }    }    while(~scanf("%d", &n)){        printf("%d\n", a[n]);    }    return 0;}