Could have a look at the following. They aren't solutions to your problem but are good for understanding different sorts quickly and also playing around with creating some.
visualgo.net/en/sorting
sorting.at

I think you got it, the worst case is 3n. In "normal" bubble sort you have to make n compares n times hence the O(n^2) to get all elements sorted. In your case, since bubble sort has a side effect of having the largest element being sorted out first and you only need 3 of those, then you would at worst have to make n compares 3 times.

I don't know how to answer your question with log(n) thingy. But in my mind, sorting the source array is not required.

What I would do:

• traverse source
• add entry from source array to target array only if bigger than any entry present in target
• sort the target (should have max 4 elements)
• remove 4th element if present (should be the smallest)
• repeat until you check each entry of source array

Not sure if it's better than sorting the source array though.

Here's what you can do Vikas Poonia, i have shared you the Algo for your question!

1) Initialize the largest three elements as minus infinite.

first = second = third = -∞

2) Iterate through all elements of array.

 a) Let current array element be x.

   b) If (x > first)
      {
          // This order of assignment is important
          third = second
          second = first
          first = x   
       }

   c)  Else if (x > second)
      {
          third = second
          second = x 
      }

   d)  Else if (x > third)
      {
          third = x  
      }

3) Print first, second and third.

Please Let me know if you have any queries, will be happy to help 😇