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Bubble Sort needs a modification

Posted on 2008-10-30
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Last Modified: 2008-10-30
I have a bubble sort script. It compares values after the first pass, the largest number is guaranteed to be in the highest -numbered element of the array; after the second pass, the two highest numbers are "in place", and so on. Instead of making nine comparisons on every pass, I need to modify the bubble sort to make eight comparisons on the second pass, seven on the third pass, and so on.

The code is attached, thank you.
#include <stdio.h>
#define SIZE 10
 
/* function main begins program execution */
int main( void )
{
	/* initialize a */
	int a[SIZE] = { 2, 6, 4, 8, 10, 12, 89, 68, 45, 37 };
	int pass; /* passes counter */
	int i; /* comparison counter */
	int hold; /* temporary location used to swap array elements */
 
	printf( "Data items in original order\n" );
 
	/* output original array */
	for ( i = 0; i < SIZE; i++ ) {
		printf( "%4d", a[ i ] );
	} /* end for */
 
	/* bubble sort */
	/* loop to control number of passes */
	for ( pass = 1; pass < SIZE; pass++ ) {
 
		/* loop to control number of comparisons per pass */
		for ( i = 0; i < SIZE - 1; i++ ) {
 
			/* compare adjacent elements and swap them if first element is greater than second element */
			if ( a[ i ] > a[ i + 1 ] ) {
				hold = a[ i ];
				a[ i ] = a[ i + 1 ];
				a[ i + 1 ] = hold;
			} /* end if */
 
		} /* end inner for */
 
	} /* end outer for */
 
	printf( "\nData items in ascending order\n" );
 
	/* output sorted array */
	for ( i = 0; i < SIZE; i++ ) {
		printf( "%4d", a[ i ] );
	} /* end for */
 
	printf( "\n" );
 
	return 0; /* indicates successful termination */
}

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Question by:Doomtomb
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Infinity08 earned 1500 total points
ID: 22845317
You only have to change the upper limit of the inner loop. Use the current value of 'pass' for that ...
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by:Doomtomb
ID: 22845396
Ok, I think I got it, now I have one last modification I have to make:

The data in the array may already be in the proper order or near-proper order, so why make nine passes if fewer will suffice? Modify the sort to check at the end of each pass whether any swaps have been made. If none are made, then the data must already be in the proper order, so the program should end. If swaps have been made, then at least one more pass is needed.

(yes this is for a class)

I have attached the new script, all that's changed from the original is on the inner loop "i = 0" to "i = pass - 1"
/* Program 8: Due 10/31/08 
Description: Bubble Sort
for Sandra Jeffers
Engineering Programming EG1304
10:20am Mon-Wed-Fri */
#include <stdio.h>
#define SIZE 10
 
/* function main begins program execution */
int main( void )
{
	/* initialize a */
	int a[SIZE] = { 2, 6, 4, 8, 10, 12, 89, 68, 45, 37 };
	int pass; /* passes counter */
	int i; /* comparison counter */
	int hold; /* temporary location used to swap array elements */
	int swap;
 
	printf( "Data items in original order\n" );
 
	/* output original array */
	for ( i = 0; i < SIZE; i++ ) {
		printf( "%4d", a[ i ] );
	} /* end for */
 
	/* bubble sort */
	/* loop to control number of passes */
	for ( pass = 1; pass < SIZE; pass++ ) {
 
		/* loop to control number of comparisons per pass */
		for ( i = pass - 1; i < SIZE - 1; i++ ) {
 
			/* compare adjacent elements and swap them if first element is greater than second element */
			if ( a[ i ] > a[ i + 1 ] ) {
				hold = a[ i ];
				a[ i ] = a[ i + 1 ];
				a[ i + 1 ] = hold;
				swap++;
			} /* end if */
 
		} /* end inner for */
 
		if ( swap == 0 )
			break;
 
	} /* end outer for */
 
	printf( "\nData items in ascending order\n" );
 
	/* output sorted array */
	for ( i = 0; i < SIZE; i++ ) {
		printf( "%4d", a[ i ] );
	} /* end for */
 
	printf( "\n" );
 
	return 0; /* indicates successful termination */
}

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by:Doomtomb
ID: 22845417
NVMD I GOT this working, sorry, I stared at this for like 30 mins and had no clue and then in like 5 mins i tried just a couple things and it worked, sorry for wasting your time, ill award points.
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Expert Comment

by:Infinity08
ID: 22845436
>> all that's changed from the original is on the inner loop "i = 0" to "i = pass - 1"

Since you do your bubble sort starting from the back (ie. the last value is put in place first), it's better to change the upper limit, rather than the lower limit like you did ;)
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