使用递归在Java中以正确格式打印菱形图案

Question

My program reads in values from a file and uses a recursive method to print patterns of asterisks based on those values. I'm just having a problem getting everything to line up properly.

The output is supposed to look like this:

    *
  *   *
*   *   *
  *   *  
    *

Regarding the format of the output, the directions are:

"Note that the pattern is aligned symmetrically (vertically) about the center line. The pattern should be aligned symmetrically on each line (horizontally) as well- hint: use the line value to help space."

But my output looks like this:

*
*  *
*  *  *
*  *
*

The code I'm using to get this pattern:

public static void makePattern(int thisRow, int num) {
    if(thisRow >= num) {
        for(int i = 0; i < num; i++) {
            System.out.print("  " + "*" + "  ");
        }
        System.out.println();

    }
    else {
        for(int i = 0; i < thisRow; i++) {
            System.out.print("  " + "*" + "  ");
        }
        System.out.println();

        makePattern(thisRow + 1, num);

        for(int i = 0; i < thisRow; i++) {
            System.out.print("  " + "*" + "  ");
        }
        System.out.println();
    }
}

Also my main method:

import java.util.Scanner;
import java.io.*;

public class Program3 {
    public static void main(String[] args) throws Exception {
        int num = 0;
        int thisRow = 1;
        java.io.File file = new java.io.File("../instr/prog3.dat");
        Scanner fin = new Scanner(file);

        while(fin.hasNext()) {
                num = fin.nextInt();
                if(num >=0 && num <= 25)
                    makePattern(thisRow, num);
                System.out.println();
        } 
        fin.close();

    }

Any suggestions on how to edit my code to make my output appear like the example pattern I included?

Answer 1

Let's analyse the output first!!

First step is to analyse the output

Conclusions:

• The total number of characters on every line is always n (=3)

• Number of Spaces has the following pattern:

  1st line 3 - 1 spaces
  2nd line 3 - 2 spaces
  3rd line 3 - 3 spaces
  4th line 4 - 3 spaces
  5th line 5 - 3 spaces

  So

   if(num < thisRow) { numberOfSpaces = thisRow - num; } else { numberOfSpaces = num - thisRow; } 

• Number of Stars is always [ n - the number of spaces ]

  So

   int numberOfStars = num - numberOfSpaces; 

• And the recursion should end on the 6th line, ie when current line number is n*2

  So the return condition in your recursive method should be

   if(thisRow == num * 2) return; 

Final Code : Putting the peices together

When we put the peices together, we get:

    public static void makePattern(int thisRow, int num) { 
        //the termination condition
        if(thisRow == num * 2) 
           return;

        //the number of spaces
        int numberOfSpaces = 0;     
        if(num < thisRow) {
          numberOfSpaces = thisRow - num;
        } else {
          numberOfSpaces = num - thisRow;
        }

        //the number of stars
        int numberOfStars = num - numberOfSpaces;

        //compose the string before printing it
        StringBuffer outputBuffer = new StringBuffer(num);
        for (int i = 0; i < numberOfSpaces; i++){
            outputBuffer.append(" ");
        }
        for (int i = 0; i < numberOfStars; i++){
            outputBuffer.append("* ");
        }

        //print the string
        System.out.println(outputBuffer.toString());

        //recursion
        makePattern(thisRow + 1, num);
   }

Answer 2

This is code for printing diamond shaped pattern using recursion technique.

    import java.io.BufferedReader;
    import java.io.IOException;
    import java.io.InputStreamReader;
    import java.util.*;
    public class patternRecursion {
    static int n,k;
    public static void main(String[] args) throws IOException{
        try(Scanner s = new Scanner(System.in)){

            n=Integer.parseInt(reader.readLine());
            k=n-1;
            printPattern(n);
        }
    }
    public static void printChar(int m,char c){
        if(m==0) return;
        try{
            printChar(m-1,c);
            System.out.print(c);

        }catch(StackOverflowError s){return;}

    }
    public static void printPattern(int m){
        if(m==0){
            return ;
        }else{

        printChar(m-1,' ');
        printChar(n-m,'#');
        printChar(n-m+1,'#');
           System.out.println();
           printPattern(m-1);
         printChar(m,' ');
         printChar(k-m,'#');
         printChar(k-m+1,'#');
            System.out.println();
         }

    }

}