Max Factor hdu2710

Problem Description

To improve the organization of his farm, Farmer John labels each of his N (1 <= N <= 5,000) cows with a distinct serial number in the range 1..20,000. Unfortunately, he is unaware that the cows interpret some serial numbers as better than others. In particular, a cow whose serial number has the highest prime factor enjoys the highest social standing among all the other cows.

(Recall that a prime number is just a number that has no divisors except for 1 and itself. The number 7 is prime while the number 6, being divisible by 2 and 3, is not).

Given a set of N (1 <= N <= 5,000) serial numbers in the range 1..20,000, determine the one that has the largest prime factor.

 

Input

* Line 1: A single integer, N

* Lines 2..N+1: The serial numbers to be tested, one per line

 

Output

* Line 1: The integer with the largest prime factor. If there are more than one, output the one that appears earliest in the input file.

 

Sample Input

4
36
38
40
42

 

Sample Output

38

 

找到最大的素数因子

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#define maxn 20003
using namespace std;
int isPrime(int n)
{
    int i;
    int b = sqrt(n);
    for(i = 2; i <= b; i++)
        if(n % i == 0)
            return 0;
    return 1;
}
int pre_solve(int n)
{
    int temp1=1;
    for(int i=1;i<=n;i++)
    {
        if(n%i==0&&isPrime(i))
        temp1=i;
    }
    return temp1;
}
int main()
{
    int ncase;
    int num,ans,maxn1,temp;
    while(~scanf("%d",&ncase))
    {
        temp=ans=maxn1=0;
        while(ncase--)
        {
            scanf("%d",&num);
            ans=pre_solve(num);
            if(ans>temp)
            {
                temp=ans;
                maxn1=num;
            }
        }
        printf("%d\n",maxn1);
    }
    return 0;
}