Java Data Structure How to - Implement a simple version of quick sort

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Question

We would like to know how to implement a simple version of quick sort.

Answer

public class MainClass {
  public static void main(String[] args) {
    int[] intArray = { 1, 9, 2, 8, 3, 7, 4, 6, 5 };
    for (int i : intArray) {
      System.out.println(i);//from   ww  w  .j a  va 2  s .c o  m
    }
    quickSort(intArray);
    for (int i : intArray) {
      System.out.println(i);
    }
  }

  public static void quickSort(int[] intArray) {
    recQuickSort(intArray, 0, intArray.length - 1);
  }

  private static void recQuickSort(int[] intArray, int left, int right) {
    if (right - left <= 0)
      return;
    else {
      int pivot = intArray[right];

      int partition = partitionIt(intArray, left, right, pivot);
      recQuickSort(intArray, left, partition - 1);
      recQuickSort(intArray, partition + 1, right);
    }
  }

  private static int partitionIt(int[] intArray, int left, int right, int pivot) {
    int leftPtr = left - 1;
    int rightPtr = right;
    while (true) {
      while (intArray[++leftPtr] < pivot)
        ;

      while (rightPtr > 0 && intArray[--rightPtr] > pivot)
        ;

      if (leftPtr >= rightPtr)
        break;
      else
        swap(intArray, leftPtr, rightPtr);
    }
    swap(intArray, leftPtr, right);
    return leftPtr;
  }

  private static void swap(int[] intArray, int dex1, int dex2) {
    int temp = intArray[dex1];
    intArray[dex1] = intArray[dex2];
    intArray[dex2] = temp;
  }
}  

The code above generates the following result.

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