What Is Insertion Sort – Complete Guide

Welcome to this deep dive into the world of programming algorithms, where we demystify one of the fundamental sorting methods—Insertion Sort. It’s an algorithm you’ve likely encountered naturally, even if you’re new to coding. Imagine you’re organizing a hand of playing cards: you’d pick a card and place it in its correct position relative to the cards you’ve already sorted. That’s Insertion Sort in essence! This tutorial is designed to guide you through the ins and outs of this algorithm with engaging examples and clear explanations, sharpening your logical thinking and coding skills, whether you’re a beginner or a seasoned programmer. Let’s sort through this together and discover why Insertion Sort is such a valuable tool in your developer toolkit.

What is Insertion Sort?

Insertion Sort is a comparison-based sorting algorithm that builds a final sorted array (or list) one element at a time. It’s like assembling a complex jigsaw puzzle by picking pieces individually and placing them in their correct spots until the whole picture is revealed.

What is it for?

This sorting algorithm is primarily used for organizing sequences—like numbers or strings—into a particular order. While it’s not the fastest on large lists compared to more advanced algorithms like Quick Sort or Merge Sort, its simplicity and efficiency on small data sets make it indispensable.

Why Should I Learn It?

Learning Insertion Sort is more about developing problem-solving abilities and understanding algorithmic concepts than about the algorithm itself. Even if newer algorithms outshine it, Insertion Sort lays a strong foundation for understanding more complex sorting methods and is a staple for any programming interview. Plus, its straightforward implementation makes it an excellent starting point for those just beginning their coding adventure.

CTA Small Image
FREE COURSES AT ZENVA
LEARN GAME DEVELOPMENT, PYTHON AND MORE
ACCESS FOR FREE
AVAILABLE FOR A LIMITED TIME ONLY

Understanding the Algorithm

To truly grasp how Insertion Sort works, let’s translate the concept into a step-by-step process. These steps serve as our algorithm’s blueprint.

  1. Start with the second element of the array (as the first element is already “sorted”).
  2. Compare this element with all its predecessors (elements to the left).
  3. If a predecessor is larger, shift it one position to the right.
  4. Repeat step 3 until you find an element smaller than the element being sorted.
  5. Insert the element in its correct position.
  6. Move to the next unsorted element and repeat steps 2-5.
  7. Continue until all elements are sorted.

Now, let’s bring this to life with some code!

function insertionSort(array) {
  for (let i = 1; i < array.length; i++) {
    let current = array[i];
    let j = i - 1;
    while (j >= 0 && array[j] > current) {
      array[j + 1] = array[j];
      j -= 1;
    }
    array[j + 1] = current;
  }
  return array;
}

This is a JavaScript implementation of Insertion Sort. We’re using a function, `insertionSort`, which takes an array as its parameter. By iterating through the array and shifting elements accordingly, we gradually create a sorted portion on the left side of the array.

Inserting the Elements

The crux of Insertion Sort lies in how we insert the elements into their correct position. The following example sheds more light on this process:

function insertionSort(array) {
  for (let i = 1; i < array.length; i++) {
    let current = array[i];
    let j = i - 1;
    while (j >= 0 && array[j] > current) {
      array[j + 1] = array[j]; // Shifting element to the right
      j--;
    }
    array[j + 1] = current; // Inserting element in the correct place
  }
  return array;
}

let numbers = [5, 2, 9, 1, 5, 6];
console.log(insertionSort(numbers));

In this example, we have a simple list of numbers. The algorithm checks each number, and if it finds any previous numbers greater than the current number, it shifts those to make room for the current number at its sorted position.

Debugging with a More Detailed Example

To clearly understand how the Insertion Sort algorithm iterates through the array, let’s examine a detailed example with explicit steps:

// Initial Array: [5, 2, 9, 1, 5, 6]
// Let's sort this step by step

// Considering 2 (index 1), 5 needs to shift:
// [5, 5, 9, 1, 5, 6] -> [2, 5, 9, 1, 5, 6]

// Considering 9 (index 2), no shifts needed as 5  [2, 2, 5, 9, 5, 6] -> [1, 2, 5, 9, 5, 6]

// And so forth until all elements are sorted

As you can step through this pseudo-code, you observe the intermediate array states that show the sequence of operations leading to a sorted array.

Analyzing Performance

One might wonder about how efficient this algorithm is. It’s time to discuss the time complexity:

– The best-case scenario: The array is already sorted, and no shifts are necessary. Here, Insertion Sort runs in O(n) time.
– The average and worst-case scenario: The array is in reverse order or is randomly sorted. Our algorithm might need to compare and shift each element multiple times, leading to a time complexity of O(n²).

// Best case scenario O(n) time complexity
let bestCase = [1, 2, 3, 4, 5];
console.log(insertionSort(bestCase));

// Worst case scenario O(n^2) time complexity
let worstCase = [5, 4, 3, 2, 1];
console.log(insertionSort(worstCase));

Through these code examples, we’ve observed how the algorithm fairs with different types of input arrays. Understanding these nuances is crucial as they can significantly impact performance in real-world applications.Great! Now that we’ve analyzed how Insertion Sort performs let’s delve into a variety of scenarios to see the algorithm in action. We’ll walk through different examples, illustrating how Insertion Sort operates on various data sets and digging into some of the common situations you might encounter.

Sorting Strings

Insertion Sort isn’t just for numbers; it works equally well on other data types, such as strings. Consider sorting an array of words by alphabetical order:

// Sorting an array of strings
let words = ["banana", "apple", "cherry"];
console.log(insertionSort(words));

function insertionSort(array) {
  for (let i = 1; i < array.length; i++) {
    let current = array[i];
    let j = i - 1;
    while (j >= 0 && array[j] > current) {
      array[j + 1] = array[j];
      j--;
    }
    array[j + 1] = current;
  }
  return array;
}

By executing this code snippet, the array of fruits gets sorted into [“apple”, “banana”, “cherry”]. Although the comparison operator changes from numerical to alphabetical, the sorting logic remains the same.

Handling Duplicate Values

Another common situation is sorting arrays with duplicate values. Though duplicates can sometimes complicate sorting logic, Insertion Sort handles them gracefully:

// Sorting an array with duplicates
let duplicates = [3, 7, 3, 1, 9, 7];
console.log(insertionSort(duplicates));

// The Insertion Sort function remains unchanged

Even with duplicates, our Insertion Sort correctly arranges the numbers into `[1, 3, 3, 7, 7, 9]`. The algorithm inherently ensures stable sorting, keeping the duplicates in the same order as they were in the input array.

Insertion Sort with Custom Comparison

Sometimes you may need to sort objects based on a particular property or using a custom comparison function. Insertion Sort is easily adaptable to accommodate this.

// Sorting an array of objects by a property
let books = [
  { title: "The Hobbit", pages: 310 },
  { title: "War and Peace", pages: 1225 },
  { title: "The Great Gatsby", pages: 180 }
];

function sortByPages(a, b) {
  return a.pages - b.pages;
}

// Adapted Insertion Sort using a comparison function
function insertionSort(array, comparator) {
  for (let i = 1; i < array.length; i++) {
    let current = array[i];
    let j = i - 1;
    while (j >= 0 && comparator(array[j], current) > 0) {
      array[j + 1] = array[j];
      j--;
    }
    array[j + 1] = current;
  }
  return array;
}

console.log(insertionSort(books, sortByPages));

Here, the books are sorted based on the number of pages, demonstrating how you can incorporate custom comparator functions to dictate the sorting behavior.

Dealing with Larger Elements

Finally, let’s see how Insertion Sort performs with larger or more complex elements, such as long strings or large numbers:

// Sorting an array of large numbers
let largeNumbers = [123456, 1234, 12345, 123, 12];
console.log(insertionSort(largeNumbers));

// Sorting an array of long strings
let longStrings = [
  "loremipsumdolorsitamet",
  "lorem",
  "loremipsum",
  "loremipsumdolo"
];
console.log(insertionSort(longStrings));

// The standard Insertion Sort function is used again

In these examples, the Insertion Sort continues to perform flawlessly, regardless of element size. It shows the versatility of the algorithm to handle different kinds and sizes of data effectively.

In conclusion, Insertion Sort is a robust, adaptable algorithm that serves as an excellent introduction to sorting methodologies. The simplicity of its implementation, combined with the depth of understanding it provides, makes it an essential part of any programmer’s toolkit. By exploring its various applications and modifications, we reinforce the importance of this fundamental algorithm in our coding repertoire.The beauty of Insertion Sort is its adaptability and straightforward implementation across numerous programming scenarios. It’s a vital tool for developers to grasp, providing a foundational understanding of algorithms. Below, we’ve included a range of code examples, further exploring Insertion Sort’s versatility.

Visualizing the Insertion Sort Process

To visualize what Insertion Sort is doing at each iteration, we can insert a logging statement within our loop:

function insertionSort(array) {
  for (let i = 1; i < array.length; i++) {
    let current = array[i];
    let j = i - 1;
    console.log("Considering element:", current);
    while (j >= 0 && array[j] > current) {
      array[j + 1] = array[j];
      console.log("Shifting", array[j]);
      j--;
    }
    array[j + 1] = current;
    console.log("Inserted", current, "into", array);
  }
  return array;
}

With the console logs placed strategically, this snippet enables learners to see how the algorithm sorts the elements live.

Optimizing for Nearly Sorted Data

Insertion Sort shines when dealing with nearly sorted data. Here’s how we could modify our algorithm for this scenario, enabling early termination when no more swaps are needed:

function optimizedInsertionSort(array) {
  for (let i = 1; i < array.length; i++) {
    let current = array[i];
    let j = i - 1;
    while (j >= 0 && array[j] > current) {
      array[j + 1] = array[j];
      j--;
    }
    if (i !== j + 1) array[j + 1] = current; // Early termination check
    else break;
  }
  return array;
}

The optimizedInsertionSort function checks if any swaps have occurred. If not, it breaks out of the loop early.

Insertion Sort for Descending Order

Sometimes we might want our data sorted in descending order. With Insertion Sort, this is a simple tweak:

function insertionSortDescending(array) {
  for (let i = 1; i < array.length; i++) {
    let current = array[i];
    let j = i - 1;
    while (j >= 0 && array[j] < current) { // Note the direction of the comparison
      array[j + 1] = array[j];
      j--;
    }
    array[j + 1] = current;
  }
  return array;
}

In this function, changing the comparison direction in the while loop ensures the sort is done in descending order.

Adding Functionality with Callbacks

We can also extend Insertion Sort to accept an optional callback function, giving the user more control over the sorting process:

function flexibleInsertionSort(array, comparisonCallback) {
  if (!comparisonCallback) {
    comparisonCallback = function(a, b) { return a - b; };
  }

  for (let i = 1; i < array.length; i++) {
    let current = array[i];
    let j = i - 1;
    while (j >= 0 && comparisonCallback(array[j], current) > 0) {
      array[j + 1] = array[j];
      j--;
    }
    array[j + 1] = current;
  }
  return array;
}

Here, we define a default comparisonCallback if none is provided, but allow for flexibility by letting the user define their own.

These variations and optimizations showcase the level of customization and efficiency that can be achieved with Insertion Sort, making it a powerful algorithm with a gamut of applications. Each adaptation allows us to see how the algorithm can be tailored to meet the unique demands of different data sets and sorting needs. As you dive into these examples and tweak them on your own, you’ll gain a deeper appreciation for the elegant simplicity of Insertion Sort and its pivotal role in sorting algorithms.

Continuing Your Learning Journey

Now that you’ve dipped your toes into the world of algorithms with Insertion Sort, your journey in mastering programming doesn’t have to end here. To further extend your knowledge and skills, diving into Python—a language celebrated for its clarity and broad applicability—is a logical next step. Our Python Mini-Degree will guide you through the coding fundamentals, take you through advanced algorithms, and even scratch the surface with game and app development. This collection of courses is crafted to ensure a smooth learning curve, whether you’re a beginner eager to write your first line of code or looking to deepen your existing coding prowess.

Furthermore, if you’re keen on exploring more areas of programming, from game creation to artificial intelligence, be sure to check out our broader range of programming courses. These courses, similar to building blocks, will help you piece together a solid foundation, enabling you to construct a robust career in technology. With over 250 courses, Zenva provides learning experiences for every step of your journey, helping you move confidently from beginner to pro. Your future in coding is bright and full of potential – keep learning, keep building, and most importantly, keep enjoying the adventure that programming offers!

Conclusion

As you’ve seen, Insertion Sort is much more than a mere algorithm—it’s a stepping stone towards a greater understanding of computer science principles and a proof of the elegance that lies in simplicity. It’s the perfect example of how starting with the basics can lead to mastering even the most complex concepts in coding. We encourage you to keep experimenting with Insertion Sort, optimize it, and adapt it to different problems to see first-hand how algorithms shape the technology we rely on every day.

Remember, this is just one fragment of the vast world of programming waiting for you to explore. Whether your interest lies in web development, data science, or game design, our Python Mini-Degree and other programming courses are here to guide your learning path. So keep pushing forward—our courses will be with you every step of the way as you transform curiosity into expertise. Let’s code a brighter future together!

Did you come across any errors in this tutorial? Please let us know by completing this form and we’ll look into it!

FREE COURSES
Python Blog Image

FINAL DAYS: Unlock coding courses in Unity, Godot, Unreal, Python and more.