Largest prime factor Time Limit:1000MS Memory Limit:32768KB 64bit IO Format:%I64d & %I64u Submit Status Practice HDU 2136 Appoint description: System Crawler (Oct 13, 2016 7:58:16 PM)
Description
Everybody knows any number can be combined by the prime number.
Now, your task is telling me what position of the largest prime factor.
The position of prime 2 is 1, prime 3 is 2, and prime 5 is 3, etc.
Specially, LPF(1) = 0.
Input
Each line will contain one integer n(0 < n < 1000000).
Output
Output the LPF(n).
Sample Input
1
2
3
4
5
Sample Output
0
1
2
1
3
每個數都可以全由質數組成,找出組成此數最大質數位置。
#include<iostream>
using namespace std;
int a[1000000];
int main()
{
int k=1;
memset(a,0,sizeof(a));
for(int i=2;i<1000000;i++)
{
if(!a[i])
{
a[i]=k;
for(int j=i+i;j<1000000;j+=i)
a[j]=k;
k++;
}
}
int n;
while(~scanf("%d",&n))
{
printf("%d\n",a[n]);
}
return 0;
}