HDU-2710 质因子

最新推荐文章于 2025-07-23 09:59:13 发布

luer9

最新推荐文章于 2025-07-23 09:59:13 发布

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分类专栏：素数

本文链接：https://blog.youkuaiyun.com/qq_40046426/article/details/79144636

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本文介绍了一种通过筛选法预处理质数，并找出一组整数中具有最大质因数的方法。该方法首先生成一系列质数，然后遍历每个待测整数的所有质因数，记录下最大的质因数。

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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

Sample Output

代码如下

#include<iostream>
#include<cstring>
using namespace std;
bool isprime[20000];
int prime[20000];
int  init()
{// 打表了 
	int i,j,num=0;
	memset(isprime,1,sizeof(isprime));
	for(i=2;i<20000;i++)
	{
		if(isprime[i]){
			prime[num++]=i;
			for(j=i+i;j<20000;j+=i){
				isprime[j]=0;
			}
		}
	}
}
int main()
{
	int t,a,i,b,n,max;
	init();
	while(scanf("%d",&t)!=EOF){
		max=-1;
		while(t--){
			scanf("%d",&a);
			b=1;
			for(i=0;prime[i]<=a;i++)
			{
				if(a%prime[i]==0)
				{
					if(b<prime[i])
					b=prime[i];
				}
			
			}	
			if(max<b){
				max=b;
				n=a;
			}
		}printf("%d\n",n);
	} return 0; 
}