hdu5108Alexandra and Prime Numbers（素数的性质）

题目链接：

huangjing

思路：每一个数都可以表示成若干个素数的乘积，那么可以对N从2一直枚举到sqrt（N），然后对每个数都能除到不能取余为止，那么后面的合数就不会除了，所以最后得到的数就是最大的质因子，然后直接N/最大的质因子，还有就是N=1的时候没有存在的数  。

题目：

Alexandra and Prime Numbers

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 259    Accepted Submission(s): 94

Problem Description

Alexandra has a little brother. He is new to programming. One day he is solving the following problem: Given an positive integer N, judge whether N is prime.
The problem above is quite easy, so Alexandra gave him a new task: Given a positive integer N, find the minimal positive integer M, such that N/M is prime. If such M doesn't exist, output 0.
Help him!

 

Input

There are multiple test cases (no more than 1,000). Each case contains only one positive integer N.
N≤1,000,000,000.
Number of cases with N>1,000,000 is no more than 100.

 

Output

For each case, output the requested M, or output 0 if no solution exists.

 

Sample Input

3456

 

Sample Output

1212

 

Source

BestCoder Round #19

 

Recommend

#include<cstdio>#include<vector>#include<iostream>#include<algorithm>using namespace std;vector<int>ans;int n;int main(){    while(~scanf("%d",&n))    {        int k=n;        ans.clear();        if(n==1) printf("0\n");        else        {            for(int i=2;i*i<=n;i++)            {                while(n%i==0)                {                    ans.push_back(i);                    n=n/i;                }            }            if(n!=1)  ans.push_back(n);            sort(ans.begin(),ans.end());            printf("%d\n",k/ans.back());        }    }    return 0;}

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