hdoj Largest prime factor

最新推荐文章于 2021-07-04 11:08:44 发布

杜庆彦

最新推荐文章于 2021-07-04 11:08:44 发布

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本文介绍了一种通过素数筛选法找到任意整数的最大质因数位置的方法，并提供了具体的C语言实现代码。

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

Sample Output

方法：

素数筛选法。

代码：

#include 
#define N 1000000
int p[N];
int main()
{
    int i, j, n, k;
    k = 1;
    p[1] = 0;
    for(i = 2; i < N; i++){
        if(p[i] == 0){
            for(j = i; j < N; j += i){
                p[j] = k;
            }
            k++;
        }
    }
    while(scanf("%d", &n) != EOF){
        printf("%d\n", p[n]);
    }
    return 0;
}