HDU 2710 Max Factor 数论 (水

Max Factor

Time Limit:1000MS     Memory Limit:32768KB     64bit IO Format:%I64d & %I64u

 

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


比较水xjb做
新风格不错 以后就这样写了

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <queue>
#include <vector>
#include <iomanip>
#include <math.h>
#include <map>
using namespace std;
#define FIN     freopen("input.txt","r",stdin);
#define INF     0x3f3f3f3f
#define lson    l,m,rt<<1
#define rson    m+1,r,rt<<1|1
typedef long long LL;

const int MAXN=20005;

int p[MAXN];

int main()
{
    //FIN
    p[1]=1;
    int cou=0;
    for(int i=2; i<=20005; i++)
    {
        if(p[i]==0)
        {
            cou++;
            for(int j=i; j<=20005; j=j+i)
            {
                p[j]=cou;
            }
        }
    }
    int n;
    while(~scanf("%d",&n))
    {
        int ans=0,pos;
        int x;
        for(int i=1;i<=n;i++){
            scanf("%d",&x);
            if(p[x]>ans)  {ans=p[x];pos=x;}
        }
        printf("%d\n",pos);

    }

}