Understanding the merge sort Algorithm: Common Pitfalls and Fixes

Discover the common issues in implementing the `merge sort` algorithm and learn how to fix them for accurate sorting results.
---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: What is wrong with this implementation of merge sort?

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding the merge sort Algorithm: Common Pitfalls and Fixes

Sorting algorithms are a fundamental part of computer science, and merge sort is one of the most well-known and efficient ones. However, when transitioning algorithms from one programming language to another, such as from Python to Go, errors can occur. Today, we will explore a common issue faced when implementing the merge sort algorithm in Go and how to resolve it for accurate sorting results.

The Problem: Incorrect Sorting Output

A user recently faced an issue when implementing the merge sort algorithm in Go. They provided the following unsorted array:

[[See Video to Reveal this Text or Code Snippet]]

But their function was returning an incorrect output:

[[See Video to Reveal this Text or Code Snippet]]

This inconsistency indicates that there’s a problem in the implementation that needs to be addressed. Let's dive into the code snippet and find out what went wrong.

The Code: Original Implementation

Here’s the original implementation provided by the user:

[[See Video to Reveal this Text or Code Snippet]]

The Issue: Object Reference Overwrites

The problem lies in how variables array, L, and M reference the same slice in Go. By manipulating array[k], the implementation inadvertently overwrites values from L, which leads to incorrect final output. This can be summarized as follows:

Shared References: L[0] references the same element as array[0]. Thus, modifying array directly corrupts the original data in L and M.

The Solution: Introduce a New Slice

The resolution to this problem is quite simple. To prevent overwriting, we need to utilize a new slice to store the merged results. Here’s the revised version of the merge_sort function:

[[See Video to Reveal this Text or Code Snippet]]

Key Changes Made:

New Result Slice: Introduced a variable result which is initialized to the size of the original array. This prevents overwriting of L or M during the merging process.

Return Statement: Modified the return statement to give back the result slice containing merged and sorted values.

Conclusion

The initial attempt at implementing merge sort in Go resulted in unintended data overwrites due to shared references. By introducing a new slice to store the merged output, we guarantee that the original datasets remain intact, leading to correct sorting results.

Understanding these nuances can significantly improve your sorting functions and prevent frustrating debugging sessions.

Now, next time you implement merge sort, remember to keep an eye on how you handle slices and references in Go!