👀 Views: 16 💬 Answers: 1 📅 Created: 2025-09-28

sorting algorithms quick-sort Java

I'm learning this framework and I'm dealing with I'm sure I'm missing something obvious here, but Working on a project where performance is key, I've implemented a custom version of quick sort in Java... The intent was to optimize for average cases with larger datasets, leveraging a median-of-three pivot selection strategy. However, during code review, my team noticed that the algorithm is not correctly sorting certain subarrays, particularly when they contain duplicate elements. Here's the core implementation: ```java public class QuickSort { public void sort(int[] arr, int low, int high) { if (low < high) { int pivotIndex = partition(arr, low, high); sort(arr, low, pivotIndex - 1); sort(arr, pivotIndex + 1, high); } } private int partition(int[] arr, int low, int high) { int pivot = arr[high]; int i = (low - 1); for (int j = low; j < high; j++) { if (arr[j] <= pivot) { i++; swap(arr, i, j); } } swap(arr, i + 1, high); return i + 1; } private void swap(int[] arr, int i, int j) { int temp = arr[i]; arr[i] = arr[j]; arr[j] = temp; } } ``` The main concern arises with input arrays like `[3, 3, 2, 1, 4]`, where the expected output is `[1, 2, 3, 3, 4]`. Instead, I see discrepancies where the duplicates are either getting misplaced or totally ignored during certain iterations. I suspected that the pivot selection might be causing an issue with how the partitioning is handled, especially considering that I'm using the last element as a pivot. To troubleshoot, I added logging statements to observe the values of `i`, `j`, and the pivot at each step: ```java System.out.println("Pivot: " + pivot + ", i: " + i + ", j: " + j); ``` However, that only provided limited insight, as it resulted in a flood of output that made it hard to pinpoint the exact moment the logic fails. As a potential fix, I tried switching the pivot to a random index, but that didn't yield the improvements I had hoped for either. Additionally, I considered modifying how duplicates are handled by implementing a three-way partitioning scheme, but I'm unsure how to effectively integrate that into my current setup. Given the complexities involved, I would appreciate any suggestions or best practices for handling sorting with potential duplicates in quick sort. Are there specific algorithm adjustments or alternative strategies that might help ensure correct ordering in these cases? For context: I'm using Java on Windows. Any ideas what could be causing this? For context: I'm using Java on macOS. This is part of a larger CLI tool I'm building. This is my first time working with Java 3.11. I appreciate any insights! For reference, this is a production REST API. Thanks for your help in advance! This is my first time working with Java 3.11. Hoping someone can shed some light on this.