Largest prime factor

Time Limit: 5000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 6700 Accepted Submission(s): 2047 

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

意思就是求给定的数n的最大质因子的序号     其中1 是 0号位     跟筛素数似的 ，可以先求出一个新素数，求这个素数的一倍二倍一直到上限范围

标记序号

#include<stdio.h>#include<string.h>#include<iostream>using namespace std;int p[1000001];int main(){int k=0,n;        memset(p,0,sizeof(p));for(int i=2;i<1000001;i++){if(!p[i]){k++;for(int j=i;j<1000001;j+=i)                 {p[j]=k;            }}}while(scanf("%d",&n)!=EOF){printf("%d\n",p[n]);}return 0;}