hdu 2710 Max Factor(找最大素数)
时间:2014-08-21 00:18:23
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题目链接:http://acm.hdu.edu.cn/showproblem.php?pid=2710
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.
(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
* 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
题意:
求给出数据含有最大质数的数,如:36 38 40 42 即19为38的最大质数,也是4个数中最大的质数。
所以输出包含最大质数的数38,还要题目最后说如果有多个,要输出最前面的那个数。
思路:
先打表出所有的素数,然后再寻找即可!
代码如下:
#include <cstdio> #include <cstring> const int MAXN = 20017; int s[MAXN]; int main() { int n,m; memset(s,0,sizeof(s)); s[1]=1;//此题1也是素数 for(int i = 2; i < MAXN; i++)//筛选所有范围内的素数 { if(s[i] == 0)//没有被更新过 for(int j = i; j < MAXN; j+=i) { s[j]=i; } } while(~scanf("%d",&n)) { int ans; int maxx = -1; for(int i = 0; i < n; i++) { scanf("%d",&m); if(s[m] > maxx) { maxx = s[m]; ans = m; } } printf("%d\n",ans); } return 0; }
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原文:http://blog.csdn.net/u012860063/article/details/38715373
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