Max Factor
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 11145 Accepted Submission(s): 3541
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
解析:采用素数筛选法,记录每个数的最大素数因子。然后直接比较。
#include<bits/stdc++.h>
using namespace std;
int f[20005];
int n,x,cnt;
int main()
{
memset(f,0,sizeof(f));
f[1]=1;//题目里的1是素数,去掉就不对了
for(int i=2; i<=20005; i++)
{
if(f[i]==0)
{
for(int j=i; j<=20005; j+=i)
f[j]=i;
}
}
while(~scanf("%d",&n))
{
int p,m=0;
for(int i=0; i<n; i++)
{
scanf("%d",&x);
if(f[x]>m)
{
m=f[x];
p=x;
}
}
printf("%d\n",p);
}
return 0;
}