Largest prime factor(素数表的巧用）

最新推荐文章于 2021-07-04 11:08:44 发布

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#ACM #水题 #数学 #素数表

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本文探讨了如何确定任意整数的最大质因数在质数序列中的位置，并提供了实现该功能的代码示例。

Problem 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

#include<stdio.h>
#include<iostream>
#include<iostream>
#include<vector>
#define Max 1000006
using namespace std;
int vis[Max];
int n;
void make_prime()
{
	pair<int,int>p;
	memset(vis,0,sizeof(vis));
	int i,j,num=1;
	for(i=2;i<Max;i++)
	{
		if(!vis[i])
		{
			vis[i]=num;
			for(j=i+i;j<Max;j+=i)
				vis[j]=num;
			num++;
		}
	}
}
int main()
{
	//freopen("b.txt","r",stdin);
	make_prime();
	while(scanf("%d",&n)==1)
		printf("%d\n",vis[n]);
	return 0;
}