使用递归进行Java乘法

Question

我正在使用递归在Java中编写一个简单的代码。我想显示用户输入的两个数字的乘积。我设法使用递归来做到这一点，但坚持在我想表明产品可以写成（例）10 * 5 = 5 + 5 + 5 + 5 + 5 + 5 + 5 + 5 + 5 + 5次（10次）或12 * 3 = 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3（12次）。这是我的代码到目前为止。在代码中，我写了一个注释，它应该被写入（例子）。谢谢。

import java.util.Scanner; 

public class RecursiveMultiplication { 

public static void main(String[] args) { 
    Scanner key = new Scanner(System.in); 
    int a, b; 
    System.out.print("Enter first number: "); 
    a = key.nextInt(); 
    System.out.print("Enter second number: "); 
    b = key.nextInt(); 
    System.out.println("The product of " + a + " and " 
      + b + " is: " + multiRec(a, b)); 
    System.out.println("It could also be written as: "); //Here should product be broken into smaller numbers 


} 

public static int multiRec(int x, int y) { 
    if (x == 0 || y == 0) { 
     return 0; 
    } else { 
     if (x == 1) { 
      return y; 
     } else { 
      return x + (multiRec(x, y - 1)); 
     } 
    } 

    } 

} 

Answer 1

一个StringBuilder应defiend为

StringBuilder buf = new StringBuilder (a); 

完成后通过这个StringBuilder的paramater为multiRec

，然后更改multiRec是

public static int multiRec(int x, int y, StringBuilder buf) { 
    if (x == 0 || y == 0) { 
     return 0; 
    } else { 
     if (x == 1) { 
      return y; 
     } else { 
      buf.append (" + ").append (x); 
      return x + (multiRec(x, y - 1, buf)); 
     } 
    } 

    } 

} 

然后，只需打印输出其价值

Answer 2

import java.util.Scanner; 

public class RecursiveMultiplication { 
    public static void main(String[] args) { 
     Scanner key = new Scanner(System.in); 
     int a , b; 
     System.out.print("Enter first number: "); 
     a = key.nextInt(); 
     System.out.print("Enter second number: "); 
     b = key.nextInt(); 
     System.out.printf("%d %s %d %s",a , "*" , b ,"= "); 
     System.out.println("\nThe product of " + a + " and " 
       + b + " is: " + multiRec(b, a)); 
     // System.out.println("It could also be written as: "); //Here should product be broken into smaller numbers 


    } 

    public static int multiRec(int x, int y) { 

     if (x == 0 || y == 0) { 
      return 0; 
     } else { 
      System.out.print(x+" "); 
      if (y == 1) { 
       return x; 
      } else { 
       System.out.print(" + "); 
       return x + (multiRec(x, y - 1)); 
      } 
     } 

     } 
}