三角递归Java [英] Triangle Recursion Java

问题描述

在命令行上输入两个数字m和n，并写出一个星号的三角形模式

  public class Triangle {
 
 public static void main（String [] args）{
 int a = 0; 
 int b = 0; 
 if（args.length！= 0）{
 a = Integer.parseInt（args [0]）; 
 b = Integer.parseInt（args [1]）; 
} 
 printFirstHalf（a，b）; 
 printSecondHalf（a，b）; 
 
 
 public static void printFirstHalf（int m，int n）{
 
 if（m == 0）{
 return; 
 
 
 //递归步骤
 for（int i = m; i <= n; i ++）{
 System.out.print（*） ; 
} 
 System.out.println（）; 
 printFirstHalf（m-1，n）; 
 
 
 
 $ b $ public static void printSecondHalf（int m，int n）{
 if（m == 0）{
 return ; 
} 
 printSecondHalf（m-1，n）; 
 
 //递归步骤
（int i = m; i< = n; i ++）{
 System.out.print（*）; 
} 
 System.out.println（）; 
 
 
 
 
 code 
 $ b 
如果3和7应该打印： 
 
 
  *** 
 **** 
 *** ** 
 ****** 
 ******* 
 ******* 
 ****** 
 ** *** 
 **** 
 *** 
  
现在打印出来：
  ***** 
 ****** 
 **** *** 
 ******* 
 ****** 
 ***** 
  
我知道我很接近，但由于某种原因，我受到严重阻碍。 
解决方案
考虑到这一点： 
 
 
  public static void printFirstHalf（int m，int n）{
 if（m> n）{
 return; 
} 
 
 //打印asterix 
（int i = 1; i <= m; i ++）{
 System.out.print（*） ; 
} 
 System.out.println（）; 
 
 //递归
 printFirstHalf（m + 1，n）; 
} 
  
你看到你现在用其他方法出错了吗？
 
 
 
如果你第一次使用递归，我明白这可能很困难，但是递归并没有魔术。逐步了解代码并理解它的功能。在这种情况下，你实际上并没有打印需要的asterix数量。坚持下去。
 
takes two numbers m and n on the command line and writes out a triangle pattern of asterisks
public class Triangle {

public static void main(String[] args) {
    int a=0;
    int b=0;
    if(args.length!=0){
        a=Integer.parseInt(args[0]);
        b=Integer.parseInt(args[1]);
    }
    printFirstHalf(a,b);
    printSecondHalf(a,b);
}

public static void printFirstHalf(int m, int n){

    if(m==0){
        return;
    }

    //recursive step
    for(int i=m; i<=n; i++){
        System.out.print("*");
    }
    System.out.println();
    printFirstHalf(m-1,n);


}

public static void printSecondHalf(int m, int n){
    if(m==0){
        return;
    }
    printSecondHalf(m-1,n);

    //recursive step
    for(int i=m; i<=n; i++){
        System.out.print("*");
    }
    System.out.println();


}
}
If 3 and 7 are sent in it should print:
***
****
*****
******
*******
*******
******
*****
****
***
Right now it prints out:
*****
******
*******
*******
******
*****
I know I am close but for some reason I am majorly stuck.  
解决方案
Consider this:
public static void printFirstHalf(int m, int n){
    if(m>n){
        return;
    }

    // print asterix
    for(int i=1; i<=m; i++){
        System.out.print("*");
    }
    System.out.println();

    // recurse
    printFirstHalf(m+1,n);
}
Do you see where you went wrong with your other method now?

If you're working with recursion for the first time, I understand that it can be difficult but there is no 'magic' with recursion. Work through the code step-by-step and understand what it does. In this case you weren't actually printing the number of asterix needed. Keep at it.

                        
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