CODEWITHSUNDEEP
c#
CinnamonBun
CinnamonBun

Reputation: 1150

Bubblesort printing out in reverse order

I've written a bubblesort, however, when I print out the array, it's sorted, but it starts off with the highest number, and ends with the lowest number.

public int[] BubbleSort(int[] unsortedArray)
{
    for(int i = 0; i < unsortedArray.Length; i++)
        for(int j = 0; j < unsortedArray.Length; j++)
            if(unsortedArray[i] < unsortedArray[j])
            {
                int temp = unsortedArray[i];
                unsortedArray[i] = unsortedArray[j];
                unsortedArray[j] = temp;
            }
    return unsortedArray;
}

Could anybody explain why the list is reversed.

EDIT: Sorry, pasted the wrong code.

When the line reads if(unsortedArray[i] < unsortedArray[j]) the list is orderded from lower to higher, however, this logically doesn't make sense. if i is lower than j, swap them.

Upvotes: 0

Views: 3779

Answers (4)

Tajwer Jalal
Tajwer Jalal

Reputation: 1

int[] bd = new int[] { 25, 35, 104, 30, 89, 30, 42, 11, 8, 4, 55, 65, 98, 542, 2 };

for (int rnd = bd.Length; rnd > 0; rnd--)
{
    for (int i = bd.Length - 1 ; i >= 0;  i--)
    {
        if (i != 0)
        {
            if (bd[i - 1] < bd[i])
            {
                temp = bd[i];
                bd[i] = bd[i - 1];
                bd[i - 1] = temp;

            }
        }
    }
}

for (int j = 0; j <= bd.Length - 1; j++)
{
    Console.Write(bd[j] + Environment.NewLine);
}

Upvotes: 0

Robert McKee
Robert McKee

Reputation: 21477

Probably better as:

public int[] BubbleSort(int[] unsortedArray)
{
    return unsortedArray.OrderBy(x=>x).ToArray();
}

A few issues with the original, i and j are iterating too much, it will still work, but it's doing unnecessary iterations that won't affect the outcome, also your conditional unsortedArray[i] < unsortedArray[j] was backwards.

public int[] BubbleSort(int[] unsortedArray)
{
    for(int i = 0; i < unsortedArray.Length-1; i++)
        for(int j = i+1; j < unsortedArray.Length; j++)
            if(unsortedArray[i] > unsortedArray[j])
            {
                int temp = unsortedArray[i];
                unsortedArray[i] = unsortedArray[j];
                unsortedArray[j] = temp;
            }
    return unsortedArray;
}

Optimized bubble sort:

public int[] BubbleSort(int[] unsortedArray)
{
    var n=unsortedArray.Length;
    while(n>0)
    {
        var newn=0;
        for(var i=1;i<=n-1;i++)
        {
            if(unsortedArray[i-1]>unsortedArray[i])
            {
                var temp = unsortedArray[i];
                unsortedArray[i] = unsortedArray[i-1];
                unsortedArray[i-1] = temp;
                newn=i;
            }
        }
        n=newn;
    }
}

Upvotes: 2

Smeegs
Smeegs

Reputation: 9224

it's this conditional

if(unsortedArray[i] < unsortedArray[j])

it should be 

if(unsortedArray[j] < unsortedArray[i])

Edit: to answer your edit.

You want the element in unsortedArray[i] to have the lowest value after the inner loop is run. Which means you only switch it out if you encounter a unsortedArray[j], that's less than the current value sitting in unsortedArray[i].

If unsortedArray[i] is already the lower value, then leave it where it is.

Upvotes: 1

KyorCode
KyorCode

Reputation: 1497

Your compare in

 if(unsortedArray[i] < unsortedArray[j])

should be

 if(unsortedArray[i] > unsortedArray[j])

Upvotes: 0

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