HDU 2710 Max Factor

http://acm.hdu.edu.cn/showproblem.php?pid=2710

Max Factor

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 1559    Accepted Submission(s): 484

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

 

 

Recommend

teddy

题意：给一组数，求这组数当中质因子最大的。1 在这个题目中也被当成素数对待。

 

#include<stdio.h>
#include<string.h>
int biao[30000];
void fun()
{
 memset(biao,0,sizeof(biao));
  int i,j;
  for(i=2;i<=29999;i++)
  {
   if(biao[i]==0)//是素数
   for(j=1;i*j<=29999;j++)
   biao[i*j]=i;//记录关于i的倍数
  }
}
int main()
{
 int T,s;
 int max1,max2;
 fun();
 while(scanf("%d",&T)==1)
 {
 max1=0;
 max2=1;//这个初始值必须是1，是0就wrong，貌似题中认为1也是素数。。
 while(T--)
 {
    scanf("%d",&s);
       if(biao[s]>max1)
          {
    max1=biao[s];
             max2=s;
          }
 }
 printf("%d\n",max2);
 }
 return 0;
}