[Algorithms] Reverse Array In Place

Learn how to reverse an array in place with this efficient, space-saving technique. In this post, we’ll explore swapping elements directly within the original array without creating a new one, practicing some key array manipulation skills along the way. Perfect for those looking to level up their JavaScript skills!

Breaking It Down

Today, let’s go over a classic problem: Reversing an Array In Place! This means we’re going to flip an array so that the elements are in reverse order—but there’s a twist. Instead of creating a new array to store the reversed elements, we’ll work directly on the original array. This approach is both efficient and helps us practice some new skills.

Here’s the plan:

1. Use the Original Array Only: We’ll swap elements within the array itself, so we’re not using any extra space.
2. No .reverse() Shortcuts: Like with other challenges, we’ll avoid any built-in reverse methods and try out our own technique.
3. Practice with Temporary Variables: We’ll use a temporary variable to hold values while we swap them around.

This approach might seem a bit tricky at first, but it’s a great way to deepen your understanding of array manipulation.

The Approach

1. Loop Through Half of the Array: By only looping halfway, we can swap the first half with the second half without repeating the process.
2. Swapping Elements: For each element in the first half, we store it temporarily, then replace it with the element from the other end. We then set the other end to the temporary variable.
3. Directly Modifying the Array: By working with the original array, we save memory and keep our code efficient.

function reverseArrayInPlace(arr) {
  for (let i = 0; i < arr.length / 2; i++) {
    const tempVar = arr[i];
    arr[i] = arr[arr.length - 1 - i];
    arr[arr.length - 1 - i] = tempVar;
  }

  return arr;
}

console.log(reverseArrayInPlace([1, 2, 3, 4, 5, 6, 7, 8])); // Output: [8, 7, 6, 5, 4, 3, 2, 1]

Summary

In this post, we tackled the “Reverse Array In Place” algorithm, learning how to flip an array by swapping elements within it without using extra space. By looping through only half of the array and using a temporary variable, we reversed the order efficiently.

This challenge not only saves memory but also strengthens your understanding of array manipulation in JavaScript.