hdu 2710

Max Factor

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 2574    Accepted Submission(s): 787

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
  

 

Source

USACO 2005 October Bronze

 

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#include <stdio.h>
#include <math.h>
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 getPrime(int n)
{
	int i, p = 1;
	for(i = 1; i <= n; i++)
		if(n % i == 0 && isPrime(i))
			p = i;
	return p;
}
int main()
{
	int n, max, a, p, maxnum;
	while(~scanf("%d", &n))
	{
		max = 1;
		maxnum = 1;
		while (n--)
		{
			scanf("%d", &a);
			p = getPrime(a);
			if(p > max)
			{
				max = p;
				maxnum = a;
			}
		}
		printf("%d\n", maxnum);
	}
	return 0;
}