Merge Sort in Java

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Introduction
Sorting is a crucial aspect of digesting data. For us humans, it’s much more natural to sort things that have something in common like the date of publishing, alphabetical order, articles belonging to an author, from smallest to largest, etc. This makes it a lot easier to comprehend the data as it’s logically connected rather than dispersed all around.
And just as important, sorted arrays are easier for computers to work with. For example, a sorted array can be searched much faster, like with the binary search algorithm, which runs in O(logn) time. An algorithm like this just doesn’t work without a sorted array.
Merge Sort
Merge sort is a divide-and-conquer algorithm, which recursively calls itself on halved portions of the initial collection.
That being said, it sounds a lot like Quicksort, which also partitions the collection and then recursively calls itself on the partitioned collections (which are typically halves).
The main difference is the fact that Quicksort is an internal, in-place sorting algorithm while Merge Sort is an external, out-of-place sorting algorithm.
This is typically done with collections which are too large to load into memory, and we load them chunk by chunk as they’re needed. So Merge Sort doesn’t need to store the whole collection into the memory from which it can easily and randomly access each and every element at any given time. Rather, the collection can be stored at an external place, such as a disk (or much longer ago – tape), from which required elements are loaded.
That being said, Merge Sort has to deal with making such loading and unloading optimal as it can get quite slow with big collections.
As mentioned above, Merge Sort is an “out-of-place” sorting algorithm. What this means is that Merge Sort does not sort and store the elements in the memory addresses of the collection given to it, but instead it creates and returns a completely new collection that is the sorted version of the one provided to it. This is an important distinction because of memory usage. For very large arrays this would be a disadvantage because the data will be duplicated, which can memory problems on some systems.
Here’s a visual representation of how it works:

Implementation
To fascilitate the algorithm, we’ll be using two methods – mergeSort() which will partition the collection and recursivelly call itself, and its helper method, merge() which will merge the results in the correct order.
Let’s start off with mergeSort():
public static void mergeSort(int[] array, int low, int high) {
if (high

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