frasette

frasette

A Common-Sense Guide to Data Structures and Algorithms, Second Edition: Are Selection Sort steps wrong? (page 71)

Hi @jaywengrow,

I think the table of Selection Sort shows wrong Max number of steps.
For example, for N = 5 we sould have:

  • Comparsions: 10 + Swaps: 2

and not:

  • Comparsions: 10 + Swaps: 4

In the following code, edit size variable to the number of element you want (5,10,20,40,80), run it to print comparsions and steps, and their sum, for a worst case scenario with a descending order array:
fiddle url: JsFiddle

function selectionSort(array) {
  let comparsions = 0;
  let swaps = 0;
  for(let i = 0; i < array.length - 1; i++) {    
    let lowestNumberIndex = i;
    for(let j = i + 1; j < array.length; j++) {
      if(array[j] < array[lowestNumberIndex]) {
        lowestNumberIndex = j;
      }
      comparsions++;
    }
 
    if(lowestNumberIndex != i) {
      swaps++;
      let temp = array[i];
      array[i] = array[lowestNumberIndex];
      array[lowestNumberIndex] = temp;
    }
  }
  let steps = "Comparsions: " + comparsions + " Swaps: " + swaps;
  console.log(steps);
  return array;
}

// code to create a sample of array size = 5,10,20,40,80
let size    = 80;
let counter = size;
let sample  = new Array(size);

for (i = 0; i < size; i++) {
   sample[i] = counter;
   counter--;
}

console.log(selectionSort(sample))

What do you think? Thanks.

Marked As Solved

jaywengrow

jaywengrow

Author of A Common-Sense Guide to Data Structures and Algorithms

Hi,

This is a really good catch! I think that for Selection Sort, the worst case scenario is still 4 swaps, but you’re right that an array in perfect descending order happens not to be the worst case scenario for Selection Sort.

An array like this: [5, 3, 1, 2, 4] - will still give you 4 swaps in Selection Sort.

I’ll have to clarify this in the next version. Thank you!

-Jay

Where Next?

Popular Pragmatic Bookshelf topics Top

jimschubert
In Chapter 3, the source for index introduces Config on page 31, followed by more code including tests; Config isn’t introduced until pag...
New
jesse050717
Title: Web Development with Clojure, Third Edition, pg 116 Hi - I just started chapter 5 and I am stuck on page 116 while trying to star...
New
New
jgchristopher
“The ProductLive.Index template calls a helper function, live_component/3, that in turn calls on the modal component. ” Excerpt From: Br...
New
hgkjshegfskef
The test is as follows: Scenario: Intersecting a scaled sphere with a ray Given r ← ray(point(0, 0, -5), vector(0, 0, 1)) And s ← sphere...
New
brunogirin
When I run the coverage example to report on missing lines, I get: pytest --cov=cards --report=term-missing ch7 ERROR: usage: pytest [op...
New
s2k
Hi all, currently I wonder how the Tailwind colours work (or don’t work). For example, in app/views/layouts/application.html.erb I have...
New
kolossal
Hi, I need some help, I’m new to rust and was learning through your book. but I got stuck at the last stage of distribution. Whenever I t...
New
New
redconfetti
Docker-Machine became part of the Docker Toolbox, which was deprecated in 2020, long after Docker Desktop supported Docker Engine nativel...
New

Other popular topics Top

New
siddhant3030
I’m thinking of buying a monitor that I can rotate to use as a vertical monitor? Also, I want to know if someone is using it for program...
New
AstonJ
Curious to know which languages and frameworks you’re all thinking about learning next :upside_down_face: Perhaps if there’s enough peop...
New
AstonJ
Thanks to @foxtrottwist’s and @Tomas’s posts in this thread: Poll: Which code editor do you use? I bought Onivim! :nerd_face: https://on...
New
New
AstonJ
In case anyone else is wondering why Ruby 3 doesn’t show when you do asdf list-all ruby :man_facepalming: do this first: asdf plugin-upd...
New
AstonJ
Continuing the discussion from Thinking about learning Crystal, let’s discuss - I was wondering which languages don’t GC - maybe we can c...
New
New
New
First poster: AstonJ
Jan | Rethink the Computer. Jan turns your computer into an AI machine by running LLMs locally on your computer. It’s a privacy-focus, l...
New

Sub Categories: