计算组合函数的Java程序

Question

对于我的编程课，我必须编写一个程序，通过使用处理输入/输出的 main 方法、计算阶乘的方法和计算组合函数的方法来计算组合函数 C(n,k) = n!/(k!*(n-k)!)。这是我的代码:

import java.util.Scanner;
public class Combinations {

    public static void factorials (int set, int objects) {
        Scanner keyboard = new Scanner(System.in);
        int n = set;
        int k = objects;
        int c = (n-k);
        int factorial1 = 1;
        int factorial2 = 1;
        int factorial3 = 1;
        while (n > 0) {
            factorial1 = factorial1 + s;
            n = n++;
        }//while loop
        while (k > 0) {
            factorial2 = factorial2 + o;
            k = k++;
        }//while loop
        while (c > 0) {
            factorial3 = factorial3 + c;
            c = c++;
        }//while loop
        System.out.println(Combinations(factorial1,factorial2,factorial3));
    }//method factorials
    public static int Combinations (int set, int objects, int x){
        int n = set;
        int k = objects;
        int c = x;
        int combination;
        combination = n/(k*c);
        return combination;
    }//method Combinations
    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        System.out.println("Enter the number of integers in a set: ");
        int n = keyboard.nextInt();
        System.out.println("Enter the number of objects to be chosen from the set: ");
        int k = keyboard.nextInt();
        System.out.println(factorials(n,k));
    }//method main

}//class

我的问题是，我收到了 System.out.println(factorials(s,o)); 的错误消息 - “PrintStream 类型中的方法 println(boolean) 不适用于参数 (void)”。我不知道为什么这么说。帮助？

Answer 1

在您的代码中，

public static void factorials(int set, int objects)
{
}

返回void。你不能使用 void 方法System.out.println(阶乘(s, o));

尝试将代码更改为

public static int factorials(int set, int objects)
{
}

另一种无需调用方法即可计算组合的方法，

        int index, numberOfItems, itemsToBeSelected, combinations;
        int factorial, temp, result;

        Scanner scanner = new Scanner(System.in);
        System.out.println("Number Of Items (n) : ");
        numberOfItems = scanner.nextInt();

        System.out.println("Items to be selected (r): ");
        itemsToBeSelected = scanner.nextInt();


        for (index = 1, factorial = 1; index <= numberOfItems; index++)    /* Calculate (numberOfItems) -> n! */
        {
            factorial = factorial * index;
        }

        for (index = 1, temp = 1; index <= itemsToBeSelected; index++)         /* Calculate (itemsToBeSelected) -> r! */
        {
            temp = temp * index;
        }

        for (index = 1, result = 1; index <= (numberOfItems - itemsToBeSelected); index++) /* Calculate (numberOfItems - itemsToBeSelected) -> (n-r)!*/
        {
            result = result * index;
        }

        combinations = factorial / (temp * result);
        System.out.println("Combinations : " + numberOfItems + "C" + itemsToBeSelected + " : " + combinations);

输出:

Number Of Items (n) : 
8
Items to be selected (r): 
3
Combinations : 8C3 : 56