// Exercise 2.3.22 (Solution published at http://algs4.cs.princeton.edu/)
package algs23;
import stdlib.*;
/* ***********************************************************************
 *  Compilation:  javac QuickX.java
 *  Execution:    java QuickX N
 *
 *  Uses the Bentley-McIlroy 3-way partitioning scheme,
 *  chooses the partitioning element using Tukey's ninther,
 *  and cuts off to insertion sort.
 *
 *  Reference: Engineering a Sort Function by Jon L. Bentley
 *  and M. Douglas McIlroy. Softwae-Practice and Experience,
 *  Vol. 23 (11), 1249-1265 (November 1993).
 *
 *************************************************************************/

public class XQuickX {
  private static final int CUTOFF = 8;  // cutoff to insertion sort, must be >= 1

  public static <T extends Comparable<? super T>> void sort(T[] a) {
    sort(a, 0, a.length - 1);
  }

  private static <T extends Comparable<? super T>> void sort(T[] a, int lo, int hi) {
    int N = hi - lo + 1;

    // cutoff to insertion sort
    if (N <= CUTOFF) {
      insertionSort(a, lo, hi);
      return;
    }

    // use median-of-3 as partitioning element
    else if (N <= 40) {
      int m = median3(a, lo, lo + N/2, hi);
      exch(a, m, lo);
    }

    // use Tukey ninther as partitioning element
    else  {
      int eps = N/8;
      int mid = lo + N/2;
      int m1 = median3(a, lo, lo + eps, lo + eps + eps);
      int m2 = median3(a, mid - eps, mid, mid + eps);
      int m3 = median3(a, hi - eps - eps, hi - eps, hi);
      int ninther = median3(a, m1, m2, m3);
      exch(a, ninther, lo);
    }

    // Bentley-McIlroy 3-way partitioning
    int i = lo, j = hi+1;
    int p = lo, q = hi+1;
    while (true) {
      T v = a[lo];
      while (less(a[++i], v))
        if (i == hi) break;
      while (less(v, a[--j]))
        if (j == lo) break;
      if (i >= j) break;
      exch(a, i, j);
      if (eq(a[i], v)) exch(a, ++p, i);
      if (eq(a[j], v)) exch(a, --q, j);
    }
    exch(a, lo, j);

    i = j + 1;
    j = j - 1;
    for (int k = lo+1; k <= p; k++) exch(a, k, j--);
    for (int k = hi  ; k >= q; k--) exch(a, k, i++);

    sort(a, lo, j);
    sort(a, i, hi);
  }


  // sort from a[lo] to a[hi] using insertion sort
  private static <T extends Comparable<? super T>> void insertionSort(T[] a, int lo, int hi) {
    for (int i = lo; i <= hi; i++)
      for (int j = i; j > lo && less(a[j], a[j-1]); j--)
        exch(a, j, j-1);
  }


  // return the index of the median element among a[i], a[j], and a[k]
  private static <T extends Comparable<? super T>> int median3(T[] a, int i, int j, int k) {
    return (less(a[i], a[j]) ?
        (less(a[j], a[k]) ? j : less(a[i], a[k]) ? k : i) :
          (less(a[k], a[j]) ? j : less(a[k], a[i]) ? k : i));
  }

  /* *********************************************************************
   *  Helper sorting functions
   ***********************************************************************/

  // is v < w ?
  private static <T extends Comparable<? super T>> boolean less(T v, T w) {
    if (COUNT_OPS) DoublingTest.incOps ();
    return (v.compareTo(w) < 0);
  }

  // does v == w ?
  private static <T extends Comparable<? super T>> boolean eq(T v, T w) {
    if (COUNT_OPS) DoublingTest.incOps ();
    return (v.compareTo(w) == 0);
  }

  // exchange a[i] and a[j]
  private static void exch(Object[] a, int i, int j) {
    Object swap = a[i];
    a[i] = a[j];
    a[j] = swap;
  }


  /* *********************************************************************
   *  Check if array is sorted - useful for debugging
   ***********************************************************************/
  private static <T extends Comparable<? super T>> boolean isSorted(T[] a) {
    for (int i = 1; i < a.length; i++)
      if (less(a[i], a[i-1])) return false;
    return true;
  }


  // test code
  private static boolean COUNT_OPS = false;
  public static void main(String[] args) {

    StdIn.fromFile ("data/words3.txt");

    String[] a = StdIn.readAllStrings();
    sort(a);

    // display results
    for (int i = 0; i < a.length; i++) {
      StdOut.println(a[i]);
    }
    StdOut.println("isSorted = " + isSorted(a));

    COUNT_OPS = true;
    DoublingTest.run (20000, 5, N -> ArrayGenerator.integerRandomUnique (N),          (Integer[] x) -> sort (x));
    DoublingTest.run (20000, 5, N -> ArrayGenerator.integerRandom (N, 2),             (Integer[] x) -> sort (x));
    DoublingTest.run (20000, 5, N -> ArrayGenerator.integerPartiallySortedUnique (N), (Integer[] x) -> sort (x));
  }

}