Quick sort: uses an insertion sort to handle subarrays of fewer than 10 cells : Sort « Collections « Java Tutorial

1. Java Tutorial
2. Collections
3. Sort

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);
    }
    quickSort(intArray);
    for (int i : intArray) {
      System.out.println(i);
    }
  }

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

  public static void recQuickSort(int[] intArray, int left, int right) {
    int size = right - left + 1;
    if (size < 10)
      insertionSort(intArray, left, right);
    else {
      double median = medianOf3(intArray, left, right);
      int partition = partitionIt(intArray, left, right, median);
      recQuickSort(intArray, left, partition - 1);
      recQuickSort(intArray, partition + 1, right);
    }
  }

  public static double medianOf3(int[] intArray, int left, int right) {
    int center = (left + right) / 2;

    if (intArray[left] > intArray[center])
      swap(intArray, left, center);

    if (intArray[left] > intArray[right])
      swap(intArray, left, right);

    if (intArray[center] > intArray[right])
      swap(intArray, center, right);

    swap(intArray, center, right - 1);
    return intArray[right - 1];
  }

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

  public static int partitionIt(int[] intArray, int left, int right, double pivot) {
    int leftPtr = left;
    int rightPtr = right - 1;
    while (true) {
      while (intArray[++leftPtr] < pivot)
        ;
      while (intArray[--rightPtr] > pivot)
        ;
      if (leftPtr >= rightPtr)
        break;
      else
        swap(intArray, leftPtr, rightPtr);
    }
    swap(intArray, leftPtr, right - 1);
    return leftPtr;
  }

  public static void insertionSort(int[] intArray, int left, int right) {
    int in, out;

    for (out = left + 1; out <= right; out++) {
      int temp = intArray[out];
      in = out;

      while (in > left && intArray[in - 1] >= temp) {
        intArray[in] = intArray[in - 1];
        --in;
      }
      intArray[in] = temp;
    }
  }
}

1
9
2
8
3
7
4
6
5
1
2
3
4
5
6
7
8
9