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Arrays and Recursion

Wed, 17 Jan 2007 11:24:43 -0700

An array containting strings of actual written code needs to be formatted. I'm not sure how to even recursively call a method so it prints the contents of an array, let alone format it's text. Not sure if I even put my methods together properly. The code only prints the first index value of the array, no recursion takes place, and the counter variable value isn't increasing. How do I recursively call the method? Can anyone help?

public static void indent(String[] code){

int counter = 0;
String spaces = " ";

System.out.print(indent(code, counter++, spaces));
}

public static String indent(String[] code, int counter, String spaces){

String tmpStr1,
tmpStr2;

if(counter == 0){
return code[counter];
}

tmpStr1 = code[counter - 1];
tmpStr2 = code[counter];

if(tmpStr1.charAt(tmpStr1.length() - 1) == '{' && counter < code.length - 1){
code[counter] = spaces + tmpStr2;
}

return code[counter];

}

}

Re: Arrays and Recursion

Wed, 17 Jan 2007 12:35:59 -0700

: An array containting strings of actual written code needs to be formatted. I'm not sure how to even recursively call a method so it prints the contents of an array, let alone format it's text. Not sure if I even put my methods together properly. The code only prints the first index value of the array, no recursion takes place, and the counter variable value isn't increasing. How do I recursively call the method? Can anyone help?
:
: public static void indent(String[] code){
:
: int counter = 0;
: String spaces = " ";
:
: System.out.print(indent(code, counter++, spaces));
: }
:
: public static String indent(String[] code, int counter, String spaces){
:
: String tmpStr1,
: tmpStr2;
:
: if(counter == 0){
: return code[counter];
: }
:
: tmpStr1 = code[counter - 1];
: tmpStr2 = code[counter];
:
: if(tmpStr1.charAt(tmpStr1.length() - 1) == '{' && counter < code.length - 1){
: code[counter] = spaces + tmpStr2;
: }
:
: return code[counter];
:
: }
:
: }
:
Recursions and arrays is quite simple. A recursive function calls itself until a certain condition is met. In case of an array the condition is nearly always the end of the array. In pseudo-code it looks something like this:

recurseExample(Array a, int counter) {
  if (counter < a.length) {
    Do something with a[counter]
    recurseExample(a, counter++); // recursiveness
  } else {
    // a[counter] is invalid, since counter >= a.length
  }
}

This example "walks" through the array from some point to the end. For example:

  recurseExample(a, 2);

processes the array from the third element to the last.
The statement "Do something with a[counter]" can be calls to another method, which performs the processing, or it can be code included in the if-then statement.
Here is a full working example of a recursive function:

int recursiveSum(int[] numbers, int index) {
  int result;
  if (index < numbers.length) {
    result = numbers[index]; // processing
    result = result + recursiveSum(numbers, index++); // recursive call
  } else {
    result = 0
  }
  return result;
}

Re: Arrays and Recursion

Thu, 18 Jan 2007 12:28:08 -0700

Here's the code I have so far. It does what it's supposed to do, I did have a bit of help with it. Could I get anyones opinion? Also one question about arrays and recursion. Is it even possible to get rid of a for loop (when it comes to printing index values of an array), and get the values of an array to print to screen using recursion?

import javax.swing.JOptionPane;

 public class Recursion {

 	public static void main (String args[]){

	   String[] code = {
	      "public class Test {",
	      "public static void main(String[] args) {",
	      "String s = \"Countdown: \";",
	      "",
	      "for (int i = 1; i <= 20; i++) {",
	      "System.out.print(i);",
	      "if (i < 20) {",
	      "System.out.print(\",\")",
	      "}",
	      "System.out.print(\"...\")",
	      "}",
	      "",
	      "System.out.println();",
	      "}",
	      "}"
	   };

	   for(int i = 0; i < code.length; i++){
	     System.out.println(code[i]);
	   }

	   System.out.println("===");

	   code = indent(code,0,0); 

	   for(int i = 0; i < code.length; i++){
	      System.out.println(code[i]);
       }
}


public static String[] indent(String[] code, int counter, int spaces){

	String pad = "";

	  if(code[counter].length() == 0){
		  counter++;
	  }

	  if(code[counter].charAt(0) == '}'){

	      spaces -=3;

      }

		for(int i = 0; i < spaces; i++){

			pad +=" ";

		}

		code[counter] = pad + code[counter];

	  if(code[counter].charAt(code[counter].length() - 1) == '{'){

		  spaces +=3;

	   }

		if(counter < code.length-1) indent(code,counter+1,spaces);
    	return code;

}
}

Zibadian,

I also wanted to thank you for all of your help, i'm not sure if you've realised that you have helped me before, a couple of months ago, many times. I wasn't able to voice my appreciation because I was out of the country for some time. But I really appreciate all the help you have given me, and value your opinion when it comes to code I write. Thanks again, and i'm sure i'll have some posts in the future and hope to hear back from you. Hope you get this.

Re: Arrays and Recursion

Thu, 18 Jan 2007 12:35:27 -0700

: Here's the code I have so far. It does what it's supposed to do, I did have a bit of help with it. Could I get anyones opinion? Also one question about arrays and recursion. Is it even possible to get rid of a for loop (when it comes to printing index values of an array), and get the values of an array to print to screen using recursion?
:
:

: import javax.swing.JOptionPane;
: 
:  public class Recursion {
: 
:  	public static void main (String args[]){
: 
: 	   String[] code = {
: 	      "public class Test {",
: 	      "public static void main(String[] args) {",
: 	      "String s = \"Countdown: \";",
: 	      "",
: 	      "for (int i = 1; i <= 20; i++) {",
: 	      "System.out.print(i);",
: 	      "if (i < 20) {",
: 	      "System.out.print(\",\")",
: 	      "}",
: 	      "System.out.print(\"...\")",
: 	      "}",
: 	      "",
: 	      "System.out.println();",
: 	      "}",
: 	      "}"
: 	   };
: 
: 	   for(int i = 0; i < code.length; i++){
: 	     System.out.println(code[i]);
: 	   }
: 
: 	   System.out.println("===");
: 
: 	   code = indent(code,0,0); 
: 
: 	   for(int i = 0; i < code.length; i++){
: 	      System.out.println(code[i]);
:        }
: }
: 
: 
: public static String[] indent(String[] code, int counter, int spaces){
: 
: 	String pad = "";
: 
: 	  if(code[counter].length() == 0){
: 		  counter++;
: 	  }
: 
: 	  if(code[counter].charAt(0) == '}'){
: 
: 	      spaces -=3;
: 
:       }
: 
: 		for(int i = 0; i < spaces; i++){
: 
: 			pad +=" ";
: 
: 		}
: 
: 		code[counter] = pad + code[counter];
: 
: 	  if(code[counter].charAt(code[counter].length() - 1) == '{'){
: 
: 		  spaces +=3;
: 
: 	   }
: 
: 		if(counter < code.length-1) indent(code,counter+1,spaces);
:     	return code;
: 
: }
: }
:

:
: Zibadian,
:
: I also wanted to thank you for all of your help, i'm not sure if you've realised that you have helped me before, a couple of months ago, many times. I wasn't able to voice my appreciation because I was out of the country for some time. But I really appreciate all the help you have given me, and value your opinion when it comes to code I write. Thanks again, and i'm sure i'll have some posts in the future and hope to hear back from you. Hope you get this.
:
:
Here's a method, which prints an array recursively:

void recursePrint(String[] stringArray, int index) {
  if (index < stringArray.length) {
    System.out.println(stringArray[index]);
    recursePrint(stringArray, index++);
  }
}

Re: Arrays and Recursion

Thu, 18 Jan 2007 14:11:18 -0700

When I implement the method as follows,

 import javax.swing.JOptionPane;

 public class A1Q3 {

 	public static void main (String args[]){

	   String[] code = {
	      "public class Ick {",
	      "public static void main(String[] args) {",
	      "String s = \"Countdown: \";",
	      "",
	      "for (int i = 1; i <= 10; i++) {",
	      "System.out.print(i);",
	      "if (i < 10) {",
	      "System.out.print(\",\")",
	      "}",
	      "System.out.print(\"...\")",
	      "}",
	      "",
	      "System.out.println();",
	      "}",
	      "}"
	   };

	   recursePrint(code,0);

	   //for(int i = 0; i < code.length; i++){
	   //  System.out.println(code[i]);
	   //}

	   System.out.println("===");

	   code = indent(code,0,0);

	   recursePrint(code,0);
	   //for(int i = 0; i < code.length; i++){
	    //  System.out.println(code[i]);
       //}
}


public static String[] indent(String[] code, int counter, int spaces){

	String pad = "";

	  if(code[counter].length() == 0){
		  counter++;
	  }

	  if(code[counter].charAt(0) == '}'){

	      spaces -=3;

      }

		for(int i = 0; i < spaces; i++){

			pad +=" ";

		}

		code[counter] = pad + code[counter];

	  if(code[counter].charAt(code[counter].length() - 1) == '{'){

		  spaces +=3;

	   }

		if(counter < code.length-1) indent(code,counter+1,spaces);
    	return code;

}

public static void recursePrint(String[] stringArray, int index) {

  if (index < stringArray.length - 1) {

    System.out.println(stringArray[index]);

    recursePrint(stringArray, index++); //line 91

  }

}

}

It prints the first index value over and over again, then just says "at A1Q3.recursePrint(A1Q3.java : 91)", which means the problems at line 91 where I call the recursion for printing the values. I'm not sure what to do, the code looks right...

Re: Arrays and Recursion

Thu, 18 Jan 2007 14:37:58 -0700

: When I implement the method as follows,
:
:

:  import javax.swing.JOptionPane;
: 
:  public class A1Q3 {
: 
:  	public static void main (String args[]){
: 
: 	   String[] code = {
: 	      "public class Ick {",
: 	      "public static void main(String[] args) {",
: 	      "String s = \"Countdown: \";",
: 	      "",
: 	      "for (int i = 1; i <= 10; i++) {",
: 	      "System.out.print(i);",
: 	      "if (i < 10) {",
: 	      "System.out.print(\",\")",
: 	      "}",
: 	      "System.out.print(\"...\")",
: 	      "}",
: 	      "",
: 	      "System.out.println();",
: 	      "}",
: 	      "}"
: 	   };
: 
: 	   recursePrint(code,0);
: 
: 	   //for(int i = 0; i < code.length; i++){
: 	   //  System.out.println(code[i]);
: 	   //}
: 
: 	   System.out.println("===");
: 
: 	   code = indent(code,0,0);
: 
: 	   recursePrint(code,0);
: 	   //for(int i = 0; i < code.length; i++){
: 	    //  System.out.println(code[i]);
:        //}
: }
: 
: 
: public static String[] indent(String[] code, int counter, int spaces){
: 
: 	String pad = "";
: 
: 	  if(code[counter].length() == 0){
: 		  counter++;
: 	  }
: 
: 	  if(code[counter].charAt(0) == '}'){
: 
: 	      spaces -=3;
: 
:       }
: 
: 		for(int i = 0; i < spaces; i++){
: 
: 			pad +=" ";
: 
: 		}
: 
: 		code[counter] = pad + code[counter];
: 
: 	  if(code[counter].charAt(code[counter].length() - 1) == '{'){
: 
: 		  spaces +=3;
: 
: 	   }
: 
: 		if(counter < code.length-1) indent(code,counter+1,spaces);
:     	return code;
: 
: }
: 
: public static void recursePrint(String[] stringArray, int index) {
: 
:   if (index < stringArray.length - 1) {
: 
:     System.out.println(stringArray[index]);
: 
:     recursePrint(stringArray, index++); //line 91
: 
:   }
: 
: }
: 
: }
:

:
: It prints the first index value over and over again, then just says "at A1Q3.recursePrint(A1Q3.java : 91)", which means the problems at line 91 where I call the recursion for printing the values. I'm not sure what to do, the code looks right...
:
Try printing the index instead to see if that increases ok. It should then output the numbers 0 to n, where n is the length-2 of the array.

Re: Arrays and Recursion

Fri, 19 Jan 2007 12:41:14 -0700

This message was edited by circuz_phreak at 2007-1-19 12:41:31

Got it working, changed it to:

public static void recursePrint(Object[] stringArray, int index) {

   System.out.println(stringArray[index]);
      
      if (index < stringArray.length - 1) {    
        recursePrint(stringArray, index + 1);
      }

Program works great, thanks!!!