Quick Sort

QuickSort.java

public class QuickSort {
  public static void main(String[] args) {
    int[] x = {6, 2, 3, 4, 5, 9, 1};
    printArray(x);

    int left = 0;
    int right = x.length - 1;

    quickSort(x, left, right);
    printArray(x);
  }

  public static void quickSort(int[] arr, int left, int right) {
    if (arr == null || arr.length == 0)
      return;

    if (left >= right)
      return;

    int middle = left + (right - left) / 2;
    int pivot = arr[middle];
    int i = left, j = right;

    while (i <= j) {
      while (arr[i] < pivot) {
        i++;
      }

      while (arr[j] > pivot) {
        j--;
      }

      if (i <= j) {
        int temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
        i++;
        j--;
      }
    }

    if (left < j)
      quickSort(arr, left, j);

    if (right > i)
      quickSort(arr, i, right);
  }

  public static void printArray(int[] arr) {
    for(int i = 0; i < arr.length; i++) {
      System.out.print(arr[i] + " ");
    }

    System.out.println();
  }
}