Quick Sort Implementation with median-of-three partitioning and cutoff for small arrays

    

public class Main {
  public static void main(String args[]) {
  }

  public static void quicksort(Comparable[] a) {
    quicksort(a, 0, a.length - 1);
  }

  static void quicksort(Comparable[] a, int low, int high) {
    int CUTOFF = 10;
    if (low + CUTOFF > high)
      insertionSort(a, low, high);
    else {
      int middle = (low + high) / 2;
      if (a[middle].compareTo(a[low]) < 0)
        swapReferences(a, low, middle);
      if (a[high].compareTo(a[low]) < 0)
        swapReferences(a, low, high);
      if (a[high].compareTo(a[middle]) < 0)
        swapReferences(a, middle, high);

      swapReferences(a, middle, high - 1);
      Comparable pivot = a[high - 1];

      int i, j;
      for (i = low, j = high - 1;;) {
        while (a[++i].compareTo(pivot) < 0)
          ;
        while (pivot.compareTo(a[--j]) < 0)
          ;
        if (i >= j)
          break;
        swapReferences(a, i, j);
      }
      swapReferences(a, i, high - 1);

      quicksort(a, low, i - 1); 
      quicksort(a, i + 1, high);
    }
  }

  public static final void swapReferences(Object[] a, int index1, int index2) {
    Object tmp = a[index1];
    a[index1] = a[index2];
    a[index2] = tmp;
  }

  private static void insertionSort(Comparable[] a, int low, int high) {
    for (int p = low + 1; p <= high; p++) {
      Comparable tmp = a[p];
      int j;

      for (j = p; j > low && tmp.compareTo(a[j - 1]) < 0; j--)
        a[j] = a[j - 1];
      a[j] = tmp;
    }
  }
}

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Quick Sort Implementation with median-of-three partitioning and cutoff for small arrays : Sort Search « Collections Data Structure « Java

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