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
johnp
Running the examples in chapter 5 c under pytest 5.4.1 causes an AttributeError: ‘module’ object has no attribute ‘config’. In particula...
New
telemachus
Python Testing With Pytest - Chapter 2, warnings for “unregistered custom marks” While running the smoke tests in Chapter 2, I get these...
New
joepstender
The generated iex result below should list products instead of product for the metadata. (page 67) iex&gt; product = %Product{} %Pento....
New
swlaschin
The book has the same “Problem space/Solution space” diagram on page 18 as is on page 17. The correct Problem/Solution space diagrams ar...
New
jskubick
I’m running Android Studio “Arctic Fox” 2020.3.1 Patch 2, and I’m embarrassed to admit that I only made it to page 8 before running into ...
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
oaklandgit
Hi, I completed chapter 6 but am getting the following error when running: thread 'main' panicked at 'Failed to load texture: IoError(O...
New
mert
AWDWR 7, page 152, page 153: Hello everyone, I’m a little bit lost on the hotwire part. I didn’t fully understand it. On page 152 @rub...
New
Henrai
Hi, I’m working on the Chapter 8 of the book. After I add add the point_offset, I’m still able to see acne: In the image above, I re...
New

Other popular topics Top

PragmaticBookshelf
Brace yourself for a fun challenge: build a photorealistic 3D renderer from scratch! In just a couple of weeks, build a ray tracer that r...
New
AstonJ
This looks like a stunning keycap set :orange_heart: A LEGENDARY KEYBOARD LIVES ON When you bought an Apple Macintosh computer in the e...
New
AstonJ
Do the test and post your score :nerd_face: :keyboard: If possible, please add info such as the keyboard you’re using, the layout (Qw...
New
DevotionGeo
The V Programming Language Simple language for building maintainable programs V is already mentioned couple of times in the forum, but I...
New
Margaret
Hello everyone! This thread is to tell you about what authors from The Pragmatic Bookshelf are writing on Medium.
1147 29994 760
New
AstonJ
If you get Can't find emacs in your PATH when trying to install Doom Emacs on your Mac you… just… need to install Emacs first! :lol: bre...
New
New
AstonJ
If you want a quick and easy way to block any website on your Mac using Little Snitch simply… File &gt; New Rule: And select Deny, O...
New
CommunityNews
A Brief Review of the Minisforum V3 AMD Tablet. Update: I have created an awesome-minisforum-v3 GitHub repository to list information fo...
New
mindriot
Ok, well here are some thoughts and opinions on some of the ergonomic keyboards I have, I guess like mini review of each that I use enoug...
New

Sub Categories: