HDU Largest prime factor

Largest prime factor

http://acm.hdu.edu.cn/game/entry/problem/show.php?chapterid=2&sectionid=1&problemid=5

Time Limit: 5000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)

Total Submission(s): 2728    Accepted Submission(s): 860

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

 

Recommend

威士忌

 

 

#include<stdio.h>
#include<string.h>

#define N 1000000

int prime[N+5];

void getPrime(){
    memset(prime,0,sizeof(prime));
    int i,j,k=1;
    for(i=2;i<=N;i++){
        if(!prime[i]){
            for(j=1;i*j<N;j++)
                prime[i*j]=k;
            k++;
        }
    }
    prime[1]=0;
}

int main(){
    int n;
    getPrime();
    while(scanf("%d",&n)!=EOF){
        printf("%d\n",prime[n]);
    }
    return 0;
}