I’ve been working on implementing the Quicksort algorithm in Java, but I seem to be encountering an issue where the array is not sorted correctly.

Here is my code:

public class QuickSort {
    
    public static void main(String[] args) {
        int[] arr = {10, 7, 8, 9, 1, 5};
        int n = arr.length;
        
        QuickSort ob = new QuickSort();
        ob.quick_Sort(arr, 0, n-1);
        
        System.out.println("Sorted array:");
        printArray(arr);
    }
    
    void quick_Sort(int[] arr, int low, int high) {
        if (low < high) {
            int pi = partition(arr, low, high);
            
            quick_Sort(arr, low, pi-1);
            quick_Sort(arr, pi+1, high);
        }
    }
    
    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] and arr[j]
                int temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
            }
        }
        
        // Swap arr[i+1] and arr[high] (or pivot)
        int temp = arr[i+1];
        arr[i+1] = arr[high];
        arr[high] = temp;
        
        return i; 
    }
    
    static void printArray(int[] arr) {
        int n = arr.length;
        for (int i = 0; i < n; i++)
            System.out.print(arr[i] + " ");
        System.out.println();
    }
}

I tried implementing the Quicksort algorithm with different pivot strategies (first element, last element, random element, median-of-three) and expected the array to be sorted correctly. However, the current implementation does not produce the expected sorted array.

I expected the array {10, 7, 8, 9, 1, 5} to be sorted into {1, 5, 7, 8, 9, 10}.

Can someone help me identify the issue with my Quicksort implementation? Specifically, I’m having trouble with the partition method.