trjhtr

I have developed a quick sort in java, that can work with both Lomuto Partition Strategy, or Hoare Partition Strategy.

Both of them sort the array correctly.

I would like to have it code reviewed to ensure I was able to correctly implement each one of those partitioning strategies.

Is there any reason to use one vs the other?

Here it is:

public class QuickSort 

 public static void main(String... args) 
 int array = 2, 3, 4, 1, 11, 5, 7, 0, 10, -1, 99, 23;
 quickSort(array);
 System.out.println(Arrays.toString(array));
 


 public static void quickSort(int array) 
 quickSort(array, 0, array.length - 1);
 

 private static void quickSort(int array, int l, int r) 
 if (l >= r) 
 return;
 
 int p = lomutoPartition(array, l, r);//hoarePartition(array, l, r);//lomutoPartition(array, l, r);
 quickSort(array, l, p - 1);
 quickSort(array, p + 1, r);
 

 private static int lomutoPartition(int array, int l, int r) 
 //pivot chosen
 int pivot = array[r];
 int i = l - 1;
 for (int j = l; j < r; j++) 
 if (array[j] < pivot) 
 i++;
 swap(array, i, j);
 
 
 swap(array, i + 1, r);
 return i + 1;
 


 private static int hoarePartition(int array, int l, int r) 
 int pivot = array[r];
 int left = l;
 int right = r;
 while (true) 
 while (array[left] < pivot) 
 left++;
 
 while (array[right] > pivot) 
 right--;
 
 if (left >= right) 
 return left;
 
 swap(array, left, right);
 
 

 private static void swap(int array, int a, int b) 
 int temp = array[a];
 array[a] = array[b];
 array[b] = temp;
 

public static void main(String... args) 
 int array = 2, 3, 4, 1, 11, 5, 7, 0, 10, -1, 99, 23;
 quickSort(array);
 System.out.println(Arrays.toString(array));

I like that you're testing your code, but you have to visually verify your program's correctness. It would be better to use a testing framework and automate that task.

private static void quickSort(int array, int l, int r) {

One letter variable names are hard to read.
It would be better to use left and right here.
Alternatively, lhs and rhs are common abbreviations for "left hand side" and "right hand side".
I don't care for them, but they're common enough that I let them slide through code reviews at work.

 int p = lomutoPartition(array, l, r);//hoarePartition(array, l, r);//lomutoPartition(array, l, r);

There's dead code here...
It happened because you're physically changing the code in order to switch between your two different strategies.
It would be better to actually implement the strategy pattern.

You could create a PartitioningStrategy like this.

interface PartitioningStrategy 
 int partition(int numbers, int left, int right);

And then have two implementations.

public class HoarePartitioningStrategy implements PartitioningStrategy 
 public int partition(int numbers, int left, int right) 
 //...
 


public class LomutoPartitioningStrategy implements PartitioningStrategy 
 public int partition(int numbers, int left, int right) 
 //...
 

Then you can decide which strategy to use in your main.

public static void main(String... args) 
 int array = 2, 3, 4, 1, 11, 5, 7, 0, 10, -1, 99, 23;
 quickSort(array, new LomutoPartitioningStrategy());
 System.out.println(Arrays.toString(array));

Nice and clean. Keeps your code open for extension, but closed for modification.