Question

我在递归地打印出包含空格和星号的三角形时遇到了麻烦。显然，可能需要使用stringbuffer或stringbuilder来计算正确的空格和星号数量，但是我有点困难。这两个三角形应该看起来像：

****  
 ***
  **
   *

和

   *
  **
 ***
****

public static String printTriangle(int num)
{
    if (num == 0) {
        return "";
    } 

    String dots = "";
    for (int i = 0; i < num; i++) {
        dots = dots + "*";
    }

    System.out.println(dots);
    return printTriangle(num-1) + dots;
}

  public static String printTriangle2(int num) {
    if (num == 0) {
        return "";
    }

    String dots = printTriangle2(num-1);
    dots = dots + ".";

    String spaces = "";
    for (int i = 0; i < num; i++) {
        spaces = spaces + " ";
    }

    String line = spaces + dots;
    System.out.println(line);
    return line;
}

这是我到目前为止所拥有的。任何帮助将不胜感激。

这是当前的输出：

****
***
**
*
 .
   ..
      ...
          ....

Answer 1

这是一个相当简单的实现：

static void printTriangle(int n, int len)
{
  if(n == len) return;

  printRow(n, len);
  printTriangle(n+1, len);
  printRow(n, len);
}

static void printRow(int n, int len)
{
  for(int i=0; i<n; i++) System.out.print(" ");
  for(int i=n; i<len; i++) System.out.print("*");
  System.out.println();
}

测试：

printTriangle(0, 4);

输出：

****
 ***
  **
   *
   *
  **
 ***
****

尽管我喜欢这样：

static void printTriangle(String s)
{
  if(!s.contains("*")) return;

  System.out.println(s);
  printTriangle(" " + s.replaceFirst("\\*", ""));
  System.out.println(s);
}

致电

printTriangle("****");

Answer 2

尝试下面的代码并用step=0调用

printTriangle(4,0)
printTriangle2(4,0)

public static String printTriangle(int num, int step)
{
    if (num == 0) {
        return "";
    } 

    String ast = "";
    for (int i = 0; i < num; i++) {
        ast = ast + "*";
    }
    String sps = "";
    for (int i = 0; i < step; i++) {
        sps = sps + " ";
    }


    System.out.println(sps+ast);
    return printTriangle(num-1, step+1) ;
}

    public static String printTriangle2(int num, int step)
{
    if (num == 0) {
        return "";
    } 

    String ast = "";
    for (int i = 0; i <= step; i++) {
        ast = ast + "*";
    }
    String sps = "";
    for (int i = 0; i < num; i++) {
        sps = sps + " ";
    }


    System.out.println(sps+ast);
    return printTriangle2(num-1, step+1) ;
}

Java三角递归

2 个答案: