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  • HDU

    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

    题意:找到数内最大的质因子,输出这个数

    代码如下:

    #include<iostream>
    #include<cstdio>
    #include<cstring>
    #include <cmath>
    #include <algorithm>
    using namespace std;
    #define n 20017
    int pri[n];
    void prime()
    {
        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;
            }
        }
    }
    int main()
    {
        prime();
        int t,x,max,maxn;
        while(~scanf("%d",&t))
        {
            max = 0;
            maxn = -1;
            for(int i = 0;i < t;i ++)
            {
                scanf("%d",&x);
                if(pri[x] > max)
                {
                    max =pri[x];
                    maxn = x;
                }
            }
            printf("%d
    ",maxn);
        }
        return 0;
    }
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  • 原文地址:https://www.cnblogs.com/lu1nacy/p/10016642.html
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