HDU-2710 Max Factor（最大质因子）_max factor csdn-优快云博客

这道题目要求求解在1到20,000范围内的N个不同整数中，哪个数具有最大的质因子。输入包含N个整数，输出具有最大质因子的数，若有多个则输出最先出现的。" 80048874,4948213,Flume深入解析：数据采集与传输机制,"['大数据', 'flume']

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Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 11601 Accepted Submission(s): 3673

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

Source

USACO 2005 October Bronze

题解：求出N个数中，有最大质因子的数。

#include<cstdio>
#include<cstring>
#include<iostream>
#include<cmath>
using namespace std;
#define n 20017
int pri[n];
void prime(){//打表
    pri[1]=1;
    for (int i=2;i<=n; i++) {
        if (!pri[i]) {
            for (int j=i;j<=n; j=j+i) {
                pri[j]=i;//更新j数中最大的素数
            }
        }
    }
    return ;
}
int main(){
    prime();
    int t,m;
    while (cin>>t) {
        int ans=0;
        int maxx=-1;
        for (int i=0; i<t; i++) {
            cin>>m;
            if (pri[m]>maxx) {
                maxx=pri[m];
                ans=m;
            }
        }
        cout<<ans<<endl;
    }
    return 0;