recursive selection sort..

**~~transgalactic2~~** · 01-13-2009

i built this code exactly like in the theory
the min function works

where is the problem
why its not sorting
??

Code:

#include <stdio.h>
int min( int num[], int i, int j );
void swap(int num[],int i,int j);
void selection_sort(int arr[], int size);
void selSort(int array[], int i,int length);

int main()
{
	int array[3];
	 array[0]=2;
	 array[1]=6;
	 array[2]=3;
     selection_sort(array,3);
     printf("%d,%d,%d\n",array[0],array[1],array[2]);

 

   return 0;
}



 
void selection_sort(int arr[], int size){
  selSort(arr,0,size);
}

void selSort(int array[], int i,int length)
{

	if (i<length)
             { 				 
			 swap(array,i,min(array,0,i));
			 selSort(array,i+1,length); 
		}

}
 

 int min( int num[], int i, int j )
{
  if ( i > 0 )
{
  if ( num[i-1] < j )
{
  return min( num, i-1, num[i-1] );
} 
else
{
  return min( num, i-1, j);
}
} 
else
{
  return j;
}
}

void swap(int num[],int i,int j)
{
int temp;
temp=num[i];
num[i]=num[j];
num[j]=temp;
}

**itCbitC** · 01-13-2009

Instead of going through so many hoops; the recursive min() you have is enough to sort the array provided you hand out pieces of it inside a for loop.

**~~transgalactic2~~** · 01-13-2009

i cant use a for loop

only recurtion

**vart** · 01-13-2009

when calling min inside min - the last parameter is an array value

when calling min inside sel_sort - the last parameter is an array index

this will not work together

you should think about better names for parameters than i,j

**~~transgalactic2~~** · 01-13-2009

the min function works
i tried it
so i dont need to look inside it

the question is whether i implemented the algorithm of the main selection_sort(int arr[], int size)
and selsort
??

**vart** · 01-13-2009

Originally Posted by transgalactic2

the min function works
i tried it
so i dont need to look inside it

the question is whether i implemented the algorithm of the main selection_sort(int arr[], int size)
and selsort
??

it works when used correcly

you are using it incorrectly

**~~transgalactic2~~** · 01-13-2009

how am i supposed to use it in this algorithm?
the minimum function find the minimum from the starting index to the end index

thats what i did

**~~transgalactic2~~** · 01-13-2009

where is the problem in the implementation of the algorithm
??

**~~transgalactic2~~** · 01-13-2009

i did it like it was told here

http://en.wikipedia.org/wiki/Selection_sort

**anon** · 01-13-2009

If I'm not mistaken you should find the minimum item in the unsorted part of the array, that is between num[i]...num[length], not num[0]...num[i].

And the minimum function appears to be wrong for reasons others have noted.

**~~transgalactic2~~** · 01-13-2009

my min function is fine
this is an example of its working fine

Code:

#include <stdio.h>
int min( int num[], int i, int j );


int main()
{
	int array[3];
	
	 array[0]=2;
	 array[1]=6;
	 array[2]=3;
    

printf("%d\n",min(array, 3,3));

 

   return 0;
}


//j is the last member in the array
//i is the number of cells
 
 int min( int num[], int i, int j )
{
if ( i > 0 )
{
if ( num[i-1] < j )
{
return min( num, i-1, num[i-1] );
} else {
return min( num, i-1, j);
}
} else {
return j;
}
}

i changed it to

Code:

swap(array,i,min(array,length,i));

but it keeps the array as it is

**~~transgalactic2~~** · 01-13-2009

it does nothing with the array

Code:

#include <stdio.h>
int min( int num[], int i, int j );
void swap(int num[],int i,int j);
void selection_sort(int arr[], int size);
void selSort(int array[], int i,int length);

int main()
{
	int array[3];
	 array[0]=2;
	 array[1]=6;
	 array[2]=3;
     selection_sort(array,3);
     printf("%d,%d,%d\n",array[0],array[1],array[2]);

 

   return 0;
}



 
void selection_sort(int arr[], int size){
  selSort(arr,0,size);
}

void selSort(int array[], int i,int length)
{

	if (i<length)
             { 				 
			 swap(array,i,min(array,length,i));
			 selSort(array,i+1,length); 
		}

}
 

 int min( int num[], int i, int j )
{
  if ( i > 0 )
{
  if ( num[i-1] < j )
{
  return min( num, i-1, num[i-1] );
} 
else
{
  return min( num, i-1, j);
}
} 
else
{
  return j;
}
}

void swap(int num[],int i,int j)
{
int temp;
temp=num[i];
num[i]=num[j];
num[j]=temp;
}

**stevesmithx** · 01-13-2009

Try tracing the program with a debugger.

**~~transgalactic2~~** · 01-13-2009

i did
it just doesnt swap anything

why?

**vart** · 01-13-2009

And what will happen if you call it like

Code:

int main()
{
	int array[3];
	
	 array[0]=2;
	 array[1]=6;
	 array[2]=3;
    

printf("%d\n",min(array, 3,0));

 

   return 0;
}

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