package algs21;
import stdlib.*;

public class Shell {

  // sort the array a[] in ascending order using Shellsort
  public static <T extends Comparable<? super T>> void sort(T[] a) {
    int N = a.length;

    // 3x+1 increment sequence:  1, 4, 13, 40, 121, 364, 1093, ...
    int h = 1;
    while (h < N/3) h = 3*h + 1;

    while (h >= 1) {
      // h-sort the array
      for (int i = h; i < N; i++) {
        for (int j = i; j >= h && less(a[j], a[j-h]); j -= h) {
          exch(a, j, j-h);
        }
      }
      assert isHsorted(a, h);
      h /= 3;
    }
    assert isSorted(a);
  }



  /* *********************************************************************
   *  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);
  }

  // exchange a[i] and a[j]
  private static <T> void exch(T[] a, int i, int j) {
    if (COUNT_OPS) DoublingTest.incOps ();
    T 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;
  }

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

  // print array to standard output
  private static <T> void show(T[] a) {
    for (T element : a) {
      StdOut.println(element);
    }
  }

  // test code
  private static boolean COUNT_OPS = false;
  public static void main(String[] args) {
    //String[] cards = In.readStrings ("data/cards.txt");
    //StdRandom.shuffle (cards);

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

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

}