Choose and divide UVA - 10375——埃式筛法+组合数阶乘运算

Think:
1埃式筛法+组合数阶乘运算
2唯一分解定理(算术基本定理)

vjudge题目链接

以下为Accepted代码

/*
Eratosthenes筛法+组合数阶乘运算
*/
#include 
#include 
#include 

using namespace std;

int tp, primes[10004], a[10004], e[10004];

void add_factorial(int n, int d);///表示把结果乘以(n!)^d,d = 1表示乘，d = -1表示除
void add_integer(int n, int d);

int main()
{
    int p, q, r, s, i, j;
    double ans;
    ///Eratosthenes筛法得到10000以内的所有素数
    memset(a, 0, sizeof(a));
    tp = 0, a[1] = 1, a[2] = 0;
    for(i = 2; i <= 10000; i++){
        if(!a[i]){
            primes[tp++] = i;
            for(j = i*2; j <= 10000; j += i){
                a[j] = 1;
            }
        }
    }
    while(scanf("%d %d %d %d", &p, &q, &r, &s) != EOF){
        memset(e, 0, sizeof(e));
        add_factorial(p, 1);
        add_factorial(q, -1);
        add_factorial(p-q, -1);
        add_factorial(r, -1);
        add_factorial(s, 1);
        add_factorial(r-s, 1);

        ans = 1.0;
        for(i = 0; i < tp; i++){
            ans *= pow(primes[i], e[i]);
        }
        printf("%.5lf\n", ans);
    }
    return 0;
}
void add_factorial(int n, int d){
    for(int i = 1; i <= n; i++)
        add_integer(i, d);
}
void add_integer(int n, int d){
    for(int i = 0; i < tp; i++){
        while(n%primes[i] == 0){
            n /= primes[i];
            e[i] += d;
        }
        if(n == 1) break;
    }
}