HDU 1164 Eddy's research I（素数打表）

Eddy's interest is very extensive, recently he is interested in prime number. Eddy discover the all number owned can be divided into the multiply of prime number, but he can't write program, so Eddy has to ask intelligent you to help him, he asks you to write a program which can do the number to divided into the multiply of prime number factor .

Input
The input will contain a number 1 < x<= 65535 per line representing the number of elements of the set.
Output
You have to print a line in the output for each entry with the answer to the previous question.
Sample Input
11
9412
Sample Output
11
2213*181

题意：

任何一个数都能拆分成质因子相乘。

题解:

把范围内的所有素数筛选出来，然后找就行了。

#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
const int maxn=1e5+5;
int prime[maxn];
int is_prime[maxn];
int sieve(int n)
{
    int cnt=0;
    for(int i=0;i<=n;i++)
        is_prime[i]=true;
    is_prime[0]=is_prime[1]=false;
    for(int i=2;i<=n;i++)
    {
        if(is_prime[i])
        {
            prime[cnt++]=i;
            for(int j=2*i;j<=n;j+=i)
                is_prime[j]=false;
        }
    }
    return cnt;
}
int main()
{
    int k=sieve(65535);
    int n;
    while(cin>>n)
    {
        bool flag=true;
        for(int i=0;i<k;i++)
        {
            while(n&&n%prime[i]==0)
            {
                n/=prime[i];
                if(flag)
                {
                    flag=false;
                    cout<<prime[i];
                }
                else
                    cout<<'*'<<prime[i];
            }
            if(!n)
                break;
        }
        cout<<endl;
    }
    return 0;
}