[javabrijon]

Where am i going wrong? this is baffling me!

public class selections {
	
	private void selectsort(int[] a){
		int large = 0;
		int length = a.length-1;
		int temp;
		for(int i = 0; i < a.length; i++){
			while(length > 0){
				if(large > a[i]){
					large = a[i];
				}
				length--;
				
			}
			temp = a[i];
			a[i] = a[length];
			a[length] = temp;
			
		}
		for(int b = 0; b < a.length; b++){
			System.out.print(a[b] + " ");
		}
	}
	
	public static void main(String[] args) {
		
		int[] a = { 23, 45, 12, 20, 10, 4, 46 };
		
		selections ss = new selections();
		ss.selectsort(a);

	}

}

This post has been edited by javabrijon: 29 October 2009 - 02:52 AM

[Momerath]

Your large variable is set wrong. And your swap is wrong.

This post has been edited by Momerath: 28 October 2009 - 09:32 PM

[javabrijon]

Momerath, on 28 Oct, 2009 - 08:29 PM, said:

Your large variable is set wrong. And your swap is wrong.

should it be if(a[i] > large) { large = a[i];

how is the swap wrong?

[Momerath]

javabrijon, on 28 Oct, 2009 - 09:37 PM, said:

should it be if(a[i] > large) { large = a[i];

What is large the 2nd time through the outer loop?

javabrijon, on 28 Oct, 2009 - 09:37 PM, said:

how is the swap wrong?

What value does i and length have when you do the swap? Try pretending you are the computer and run through each line of code recording what each variable is at each line. Use the numbers 2, 3, 1 for your array to sort.

[javabrijon]

javabrijon, on 28 Oct, 2009 - 09:37 PM, said:

Momerath, on 28 Oct, 2009 - 08:29 PM, said:

Your large variable is set wrong. And your swap is wrong.

should it be if(a[i] > large) { large = a[i];

how is the swap wrong?

definetly not getting this!..

[macosxnerd101]

Basically, Selection Sort works by finding the maximum value in the list and swapping it with the last value. It then looks at the list, excluding the last element, repeating this process until it has reached the first element. If I was you, I would start your outer for loop at the end of the array, decrementing to 0; and change your inner loop to a for loop, iterating from 0 to length-i-1. From there, find the max element and store its index in the max field and go from there.

I actually wrote a snippet on this if you want to check it out!

This post has been edited by macosxnerd101: 29 October 2009 - 06:35 AM

[javabrijon]

macosxnerd101, on 29 Oct, 2009 - 05:33 AM, said:

Basically, Selection Sort works by finding the maximum value in the list and swapping it with the last value. It then looks at the list, excluding the last element, repeating this process until it has reached the first element. If I was you, I would start your outer for loop at the end of the array, decrementing to 0; and change your inner loop to a for loop, iterating from 0 to length-i-1. From there, find the max element and store its index in the max field and go from there.

I actually wrote a snippet on this if you want to check it out!

where can i find the snippet?

[macosxnerd101]

Hit the link under my name says My Contributions. It will take you to a page with a list of snippets I've submitted. Selection Sort is there.

[javabrijon]

macosxnerd101, on 29 Oct, 2009 - 03:13 PM, said:

Hit the link under my name says My Contributions. It will take you to a page with a list of snippets I've submitted. Selection Sort is there.

if you didnt see i commented on your selection sort ..just mainly needto know what "i" is in the first loop.

for(max = 1, n = x.length-1; i < n; n--){
		 for(int j = 0; j < n; j++){
			  if(x[j] > x[max]) max = j;
			  }
		 int temp = x[max];
		 x[max] = x[n];
		 x[n] = temp;  
	  }

[macosxnerd101]

Take another look at the snippet.

[javabrijon]

macosxnerd101, on 29 Oct, 2009 - 04:06 PM, said:

Take another look at the snippet.

i get an "i is unresolved" message on eclipse;

for(max = 1, n = x.length-1; i < n; n--){   
		 ...  
	  }

[macosxnerd101]

It appears I made a mistake when submitting it a couple months ago, and it got past inspection (which it probably shouldn't have). I've revised it. Sorry for the inconvenience!

public void selectionSort(int[] x){
   for(int max = 1, n = x.length-1; n > 0; n--){
		 for(int j = 0; j < n; j++){
			  if(x[j] > x[max]) max = j;
			  }
		 int temp = x[max];
		 x[max] = x[n];
		 x[n] = temp;  
	  }
	  
}

[javabrijon]

macosxnerd101, on 29 Oct, 2009 - 04:35 PM, said:

It appears I made a mistake when submitting it a couple months ago, and it got past inspection (which it probably shouldn't have). I've revised it. Sorry for the inconvenience!

public void selectionSort(int[] x){
   for(int max = 1, n = x.length-1; n > 0; n--){
		 for(int j = 0; j < n; j++){
			  if(x[j] > x[max]) max = j;
			  }
		 int temp = x[max];
		 x[max] = x[n];
		 x[n] = temp;  
	  }
	  
}

all good.

 public class selections {
	
	private void selectsort(int[] a){
		int max;
		int length;
		int temp;
		for(max = 1, length = a.length-1;  length > 0; length--){
			for(int j = 0; j < length; j++){
				if(a[j] > a[max]){
					max = j;
				}
			}
			temp = a[max];
			a[max] = a[length];
			a[length] = temp;
			
		}
		for(int b = 0; b < a.length; b++){
			System.out.print(a[b] + " ");
		}
	}
	
	public static void main(String[] args) {
		
		int[] a = { 23, 45, 12, 20 };
		
		selections ss = new selections();
		ss.selectsort(a);

	}

}

my array is {23, 45, 12, 20}

Quote

output: "20 12 23 45 "

.. still not working

[macosxnerd101]

Sorry for the runaround. This will work:

public static void selectionSort(int[] x){
   	  for(int i = x.length-1; i > -1; i--){
   		  int max = i;
   		  for(int j = 0; j < i; j++){
   			  if(x[j] > x[max]) max = j;
   			  }
   		  int temp = x[i];
   		  x[i] = x[max];
   		  x[max] = temp;
   		  }//end i
   		   	
	  }
   

[javabrijon]

macosxnerd101, on 30 Oct, 2009 - 08:56 AM, said:

Sorry for the runaround. This will work:

public static void selectionSort(int[] x){
   	  for(int i = x.length-1; i > -1; i--){
   		  int max = i;
   		  for(int j = 0; j < i; j++){
   			  if(x[j] > x[max]) max = j;
   			  }
   		  int temp = x[i];
   		  x[i] = x[max];
   		  x[max] = temp;
   		  }//end i
   		   	
	  }
   

cheers mate, funny thing is i solved it a couple days ago, same code aswell. (well after your previous code that is) gave me a good hint