计算有序和无序排列-C

Question

尝试计算C中的数字和选择的有序排列和无序排列。递归阶乘函数有效，排列结果提供随机存储位置

。/排列
输入项目数：5
输入编号以选择：2
有1.＃INF00个有序排列
有1.＃INF00个无序排列

#include <stdio.h>

double ordered_permutation(double total_items, double selection);
double unordered_permutation(double total_items, double selection);
double factorial( double number);

int main() {

    double items;
    double selection;
    printf("Enter number of items: ");
    scanf("%f", &items);
    printf("Enter number to select: ");
    scanf("%f", &selection);

    double ordered_perm;
    double unordered_perm;
    ordered_perm = ordered_permutation( items, selection );
    unordered_perm = unordered_permutation( items , selection );

    printf("There are %f ordered permutations\nThere are %f unordered permutations\n", ordered_perm, unordered_perm);

    return 0;
}

/*    total_items!/ ( total_items! - selection! )    */
double ordered_permutation(double total_items, double selection){
    double permutations;

    permutations = factorial(total_items)/ ( factorial(total_items) - factorial(selection) );

    return permutations;
}

/*    total_items!/ ( ( total_items! - selection! ) selection! )    */
double unordered_permutation(double total_items, double selection){
    double permutations;

    permutations = factorial(total_items)/ ( ( factorial(total_items) - factorial(selection) ) * factorial(selection));

    return permutations;
}

double factorial( double number){
    if( number <= 1 )
        return 1;
    else 
        return  number * factorial((number-1));
}

Answer 1

将分母调用更改为：

    factorial(total_items - selection)

和

    (factorial(total_items- selection) * factorial(selection))

Answer 2

这并不是您问题的答案，但是使用递归计算大型阶乘可能会导致堆栈溢出[并且相对较慢]。

另外，您将double用作计数和索引。 阶乘基于整数相乘，结果只能是整数。

这是一个非递归阶乘函数：

#if 1
typedef int value_t;
#else
typedef long long value_t;
#endif

value_t
factorial(value_t n)
{
    value_t i;
    value_t f;

    f = 1;

    for (i = 1;  i <= n;  ++i)
        f *= i;

    return f;
}