hdu2710Max Factor(水题)

Max Factor

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 6283    Accepted Submission(s): 2056

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

436384042

 

Sample Output

38

 

题意：给你n个数，求素因子最大的那个数，如果素因子大小相同，结果为最小的那个数

思路：素数筛法，然后逐个求出最大的因数

code：

#include <stdio.h>#include <string.h>int main(){    int t,prim[20000],i,j,a,max,maxn;    memset(prim,0,sizeof(prim));    prim[1]=prim[2]=prim[3]=0;    for(i=3;i<=20000;i++)    {            for(j=i*2;j<=20000;j+=i)                prim[j]=1;    }    while(scanf("%d",&t)>0)    {            max=0;            maxn=0;            for(i=0;i<t;i++)            {                scanf("%d",&a);                for(j=a;j>0;j--)                {                    if(!prim[j])                    {                        if((a%j==0)&&(j>max))                        {                            max=j;                            maxn=a;                            break;                        }                    }                }            }        printf("%d\n",maxn);    }    return 0;}

思路很简单，但写的时候出现了一些小问题，调了很久擦 。。。