在 Java 中使用递归的阶乘 [英] Factorial using Recursion in Java

问题描述

我正在使用 Java: The Complete Reference 一书学习 Java.目前我正在研究递归主题.

请注意:stackoverflow 上也有类似的问题.我搜索了它们，但没有找到我的问题的解决方案.我对以下程序中的逻辑感到困惑.

如果我运行下面的程序，它会产生正确的输出，但我不明白其中的逻辑.

• 我不明白下面这行的逻辑:result = fact(n-1) * n;
• 据我所知，如果我们传递 n=4 的值，如下面的程序所示，
• 然后，3 * 4 存储在结果中，即 12.
• 再次调用 fact(n-1).然后 n 变为 3.
• 然后将 2 * 3 存储在结果中，替换之前的 12.

• 我想你明白我的困惑/困惑在哪里.

• 谢谢.

<块引用>

类计算{事实上(int n){整数结果；如果(n==1)返回 1；结果 = 事实(n-1)* n；返回结果；}}公共类阶乘{公共静态无效主(字符串参数[]){计算 obj_one = new Calculation();int a = obj_one.fact(4);System.out.println("这个数的阶乘是:" + a);}}

解决方案

result 是 fact 方法的局部变量.因此，每次调用 fact 方法时，结果都存储在与上一次调用 fact 不同的变量中.

所以当以 3 为参数调用 fact 时，你可以想象它的结果是

 result3 = fact(2) * 3结果3 = 结果2 * 3结果 3 = 1 * 2 * 3

I am learning Java using the book Java: The Complete Reference. Currently I am working on the topic Recursion.

Please Note: There are similar questions on stackoverflow. I searched them but I didn't find the solution to my question. I am confused with the logic in the following program.

If I run the below program, it produces the correct output, but I didn't understand the logic.

• I didn't understand the logic in the following line : result = fact(n-1) * n;
• From my knowledge, If we pass the value of n=4 as shown in the below program,
• Then, 3 * 4 is stored in the result i.e., 12.
• Again, fact(n-1) is called. Then n becomes 3.
• Then the 2 * 3 is stored in the result replacing the previous 12.

• I think you understood where I am stuck up/confused.

• Thank you.

class Calculation
{
    int fact(int n)
    {
        int result;

       if(n==1)
         return 1;

       result = fact(n-1) * n;
       return result;
    }
}

public class Factorial
{
     public static void main(String args[])
     {
       Calculation obj_one = new Calculation();

       int a = obj_one.fact(4);
       System.out.println("The factorial of the number is : " + a);
     }
}

解决方案

result is a local variable of the fact method. So each time the fact method is called, the result is stored in a different variable than the previous fact invocation.

So when fact is invoked with 3 as argument, you can imagine that its result is

 result3 = fact(2) * 3
 result3 = result2 * 3
 result3 = 1 * 2 * 3

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