HDU 2136 Largest prime factor

最新推荐文章于 2018-07-15 13:30:00 发布

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本文介绍了一个算法，用于找出任意正整数的最大质因数的位置，并提供了完整的C++实现代码。通过预先计算并存储每个数的最大质因数的位置，可以高效地处理多个输入请求。

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
3

Author
Wiskey

Source
HDU 2007-11 Programming Contest_WarmUp

#include <stdio.h>
using namespace std;

int a[1000000] = {0};
int main()
{
    int count = 1;                  //记录素数的位置
    for(int i = 2; i<1000000; i++)
    {
        if(a[i]==0)
        {
            a[i] = count;
            for(int j = 2; j*i<1000000; j++)
            {
                a[i*j] = count;     //将包含i的数全部赋值为count
            }
            count++;
        }
    }
    int n;
    while(~scanf("%d",&n))
    printf("%d\n",a[n]);
}