Bubble Sort so that all numbers ending in the digit 5 comes in ascending order

Question

I am trying to implement a bubblesort of an array of integers so that all numbers ending in digit 5 comes first (ascending order), followed by all numbers which do not end in 5 (ascending order).

Before BubbleSort: [5, 1, 23, 45, 65, 89, -85, -76]

After Bubblesort (ending digit 5 (ascending order)): [-85, 5, 45, 65, -76, 1, 23, 89]

So I do know how to write the standard Bubblesort but I can't wrap my mind around the additional rule (ending in digit 5). Any help is appreciated.

Thanks

Answer 1

The only thing that needs to change is the compare code.

Assuming bubble sort code is working and uses a simple compare like:

if (a < b) ...

Create function as below. a%10 will result in values -9,-8,...,8,9 . Test when this result is 5 or -5 . The below tests when the |a%10| == 5 |a%10| == 5 .

// Return 1 when a should come before b in the array.
int cmp5(int a, int b) {
  int a5 = abs(a%10) == 5;
  int b5 = abs(b%10) == 5;
  // Since a and b are the same "five-ness", do a simple compare
  if (a5 == b5) return a < b;
  if (a5) return 1;
  return 0;
  // Could replace above 2 lines with `return a5;`
}

and call

 if (cmp5(a,b)) ...

Answer 2

As you said you know standard bubble sort, good now do the following

1. Take two arrays/vector (the one which you prefer)

2. one for multiples of 5 and other for remaining

3. Now just make standard bubble sort function bubblesort(array[])

4. Filter the inputs to the two arrays

5. After filtering make a call to bubble sort and you are done
6. And put the both results together