[JKCalhoun]

The appeal of bubble sort for me is that is it the only one I understand well enough to implement myself without having to think much about it.

[somat]

For me it's lsb radix, Yeah I know it only works on numbers, but much younger me independently invented it when slinging 3480 mainframe tape as a grave shift operator. The company had invested in mainframes early and by the time I had got there was was slightly disfunctional, they still had mainframe operators and we would run the nightly batch jobs to process orders. While they had a hard drive(the ramac) they never liked to update their programs to use it, so every major step of the process would read a tape and write a new tape(they used the tapes sort of like a massively inefficient version control, so the process could be restarted at any point) at the end of the night we would have to file a couple hundred tapes back in the library. As I hated randomly seeking through the library and was bad at ad hock sorting I put together a manual sorting routine so the numbered tapes could go back in order. What ended up working best for me I found out later was the good ol' LSB radix sort and I have a soft spot for it to this day.

[bxparks]

I read this all the time from other people, but for me, Selection sort is the easiest to remember and implement. My next easiest would be Insertion sort.

Bubble sort doesn't click for me easily. I think it's because the terminating condition seems uglier than Selection sort or Insertion sort. I always have a little voice in the back of my mind, "Is this outer loop guaranteed to terminate?"

[archargelod]

Terminating condition in Bubble sort is "did we swap any values during this loop"? Yes -> continue, No -> list is already sorted, exit the loop.

I don't believe that insertion/selection sort is easier to grasp. Can you type it from memory, without looking it up? Here's bubble sort:

    var swapped = true
    while swapped:
      swapped = false
      for i in 0 .. list.len-2:
        if list[i] > list[i+1]:
          swap(list[i], list[i+1])
          swapped = true

[bxparks]

Different strokes for different folks I guess.

Selection sort was the first sorting algorithm that I ever created: Find the smallest element for slot #1. Find the next smallest for slot #2. And so on. I've recreated it from scratch many times. The double for-loop means that it is guaranteed to finish, and it is obviously O(N^2).

I did not learn about Bubble sort until my university class, where I thought, this is a terrible algorithm: It's not completely obvious that it will finish, and it's not obvious what the runtime complexity is. For example, if the inner loop used ">=" instead of ">", it would work for test data sets with unique elements, then hang forever with a real data set that contained duplicates.

[minitech]

> Can you type it from memory, without looking it up?

Well, yeah, but that’s not a very useful heuristic for people who are already aware of the algorithms in question. If you ask people to come up with a way from scratch – probably without explicitly asking, in order to get better success, like by watching how they sort cards – I bet they won’t tend to come up with bubble sort. Maybe that says something about the relative intuitiveness of the approaches? Or not.

[3eb7988a1663]

I recall "inventing" bubble sort during one of my first CS classes when the question was posed of how to sort a list. So, not that outlandish.

[avmich]

Agree. I remember the names of many of these algorithms, but not the logic.

[jeltz]

Let's see.

  for i in 1 .. list.len - 1:
    j = i - 1
    while j >= 0 and list[j] > list[j + 1]:
      swap(list[j], list[j + 1])
      j = j - 1

[hmng]

As others have said, it is easy enough for a child in the 80s, with only a BASIC manual to come up with it. Been there, done that. Didn't even had a name for it. Later I read a magazine explaining several algorithms and found the name of what I had implemented.

For the curious, the ZX Spectrum microdrive listed files on the cartridges by order found on tape. I wanted to display it in alphabetical order like the "big" computers did.

[JKCalhoun]

Ha ha, yeah, it was in high school, in BASIC, on an Apple II that I learned how to write a bubble sort.

[ExtremisAndy]

I felt this comment in my soul. I’ll never understand it: I’ve written thousands of lines of code (as a hobbyist) to solve all sorts of problems I’ve run into and yet always seem to struggle to wrap my mind around the core algorithms any real developer should be able to handle easily. This is why I’ve never pursued programming as a career.

[vbezhenar]

It took computer scientists of the past, a lot of effort to come up with these complicated algorithms. They are not easy or trivial. They are complicated and that's OK that you can't just quickly understand them. Your imaginary "real developer" at best memorised the algorithms, but that hardly differs from smart monkey, so probably not something to be very proud of.

It is your choice which career to pursue, but in my experience, absolute majority of programmers don't know algorithms and data structures outside of very shallow understanding required to pass some popular interview questions. May be you've put too high artificial barriers, which weren't necessary.

To be a professional software developer, you need to write code to solve real life tasks. These tasks mostly super-primitive in terms of algorithms. You just glue together libraries and write so-called "business-logic" in terms of incomprehensible tree of if-s which nobody truly understands. People love it and pay money for it.

[melagonster]

Thanks for your kind comment! I do not have any systematic leaning of computer science; I often feel confused when reading textbooks on algorithms hahaha.

Should I be familiar with every step of Dijkstra’s search algorithm and remember the pseudocode at all times? Why don’t the textbooks explain why the algorithm is correct?

[monadgonad]

> Should I be familiar with every step of Dijkstra’s search algorithm and remember the pseudocode at all times?

Somehow, I think you already know the answer to that is "no".

I've been working as a software engineer for over 8 years, with no computer science education. I don't know what Dijkstra's search algorithm is, let alone have memorised the pseudocode. I flicked through a book of data structures and algorithms once, but that was after I got my first software job. Unless you're only aiming for Google etc, you don't really need any of this.

[chopin]

You should know the trade-offs of different algorithms, though. Many libraries let you choose the implementation for a spcific problem. For instance tree vs. hash map where you trade memory for speed.

[minitech]

> Why don’t the textbooks explain why the algorithm is correct?

The good ones do!

> Should I be familiar with every step of Dijkstra’s search algorithm and remember the pseudocode at all times?

If it’s the kind of thing you care to be familiar with, then being able to rederive every step of the usual-suspect algorithms is well within reach, yes. You don’t need to remember things in terms of pseudocode as such, more just broad concepts.

[mamcx]

Something that helps, I think, is to make something practical that demands it.

I used to think alike (I'm +30 year programing) until I decide to do https://tablam.org, and making a "database" is the kind of project where all this stuff suddenly is practical and worthwhile.

[tzs]

That surprises me. Selection sort seems like it should be easier to understand than bubble sort.

[JKCalhoun]

I haven't investigated selection sort. You have me curious though. Is that a step down from bubble sort? If so, maybe it's just as well I figured out bubble.

[tzs]

Selection sort is arguably the easiest sort, and arguably the easiest to see that it is correct. Given an array a with n elements A[0], A[1], ..., A[n-1], let the notation A[x:y] mean the set {A[x], A[x+1], ..., A[y]}.

  for i = 0 to n-1
    find an index j in A of the smallest member of A[i:n-1]
      swap A[i] with A[j]

I think that selection sort is easy to understand and easier to see that it is correct because it can be separated into a two array version. Given input array A and an empty array B, do this:

  while A is not empty
    find a smallest element of A
      append that to B

The in place version earlier is essentially that, just storing B and A together in one array.

That is something most non-programmers could easily come up with for physical sorting. For instance you have a row of books on a shelf that are in random order, and you want to move them to another shelf and have them sorted by author's last name.

1. Scan the first row to find the book that should come before all the rest on that row.

2. Move it to the end of the books on the second row.

3. Repeat until all the books have been moved.

Selection sort is in a sense just a computer implementation of a procedure that ordinary people have a good chance of coming up with when they need to sort physical items.

Selection sort performs better than bubble sort on random data. They are both O(n^2) but selection sort will perform fewer writes.

If you deal with data that is mostly already sorted though then bubble sort with early stopping is O(n) and wins.

With bubble sort I can't think of a two array version that makes it easier to understand. I also don't think many ordinary people would come up with bubble sort when sorting say their bookshelf.

There's also insertion sort. The two array version would be

  while A is not empty
    take the first element of A
      insert that into B keeping B sorted

In bookshelf form

1. Pick a book from the first row.

2. Find where that belongs in alphabetical order in the second row and put it there.

3. Repeat until you run out of books on the first row.

I think this is what most ordinary people who don't come up with selection sort would come up with.

The two array form can be converted to in place the same as selection sort.

Insertion sort is, like the others O(n^2). Like selection sort it is faster than bubble sort on random data. Unlike selection sort whose runtime is about the same no matter how the data is ordered, it is fast on almost sorted data.

Here's all three (bubble, selection, insertion) illustrated by folk dancers:

https://www.youtube.com/watch?v=Iv3vgjM8Pv4

https://www.youtube.com/watch?v=hFhf9djnM5A

https://www.youtube.com/watch?v=QdQmAdyfmDI

[anothernewdude]

Perhaps a sign of the trauma from university, but for me that's quicksort.

[another_twist]

Merge and Quicksort are good ones too. Quicksort esp since the idea has a flavour of "I could come up with that". Its a beautiful algorithm.

[strken]

I understand merge sort enough to just jump in and write it. It does require a little more space and thought than bubble sort, though.

[vlovich123]

Insertion sort and radix sort are also quite easy to understand, perhaps even more so.