Java中的数学（组合学）

Question

我的问题是：

我的数学公式是： 在这种情况下，X = N； Y = L; U = K;

    public class Play {

    public static void main(String args[]) {
         //n!(n−k−1)!
        int n = 10;
        int k =2;
        int l = 12;


        long result;
        result = (calculaFator(n) / calculaFator(n-k-1));
        result= (long) (result * Math.pow((n-k),(l-k)-1));
        System.out.println(result);


    }

    public static long calculaFator(long x) {
        long f = x;

        while (x > 1) {

            f = f * (x - 1);

            x--;
        }
        return f;
    }
}

应该是721599986，但它给了我96636764160

我有一些样本：

在n = 10，k = 2，l = 12的情况下应该是721599986

在n = 10，k = 2，l = 16的情况下应该是626284798

在n = 10，k = 1，l = 20的情况下应该是674941304

在n = 5，k = 2，l = 8的情况下应为10800

Answer 1

Java代码根据您指定的公式运行。 看来公式是错误的，而不是代码。 （或预期结果，或者您映射到n，l，k的x，u，y不正确？）

int x = 10;
int u = 2;
int y = 12;
long numerator = calculaFator(x);
long denominator = calculaFator(x - u - 1);

int xu1 = x - u - 1;
long result = numerator / denominator;
System.out.println();
System.out.println(x + "!= numerator: " + numerator);  //10!= numerator: 3_628_800 
System.out.println(xu1 + "!= denominator: " + denominator); //7!= denominator: 5_040 
System.out.println("result1: " + result); //result1: 720 (correct)

int xu = x - u;
int yu1 = y - u - 1;
double remainderPlaylist = Math.pow(xu, yu1);
System.out.println(xu + "^" + yu1 + " = " + remainderPlaylist);//8^9 = 1.34217728E8 
System.out.println(xu + "^" + yu1 + " = " + (long) remainderPlaylist);//8^9 = 134_217_728   (correct)

long mul = (long) (result * remainderPlaylist);
System.out.println(result + "x" + (long)remainderPlaylist + " = " + mul); //720x134_217_728 = 96_636_764_160  (mathematically correct)