// Exercise 2.2.11 (Solution published at http://algs4.cs.princeton.edu/)
package algs22;
import stdlib.*;
/* ***********************************************************************
 *  Compilation:  javac MergeX.java
 *  Execution:    java MergeX < input.txt
 *  Dependencies: StdOut.java StdIn.java
 *  Data files:   http://algs4.cs.princeton.edu/22merge/tiny.txt
 *                http://algs4.cs.princeton.edu/22merge/words3.txt
 *
 *  Sorts a sequence of strings from standard input using an
 *  optimized version of mergesort.
 *
 *  % more tiny.txt
 *  S O R T E X A M P L E
 *
 *  % java MergeX < tiny.txt
 *  A E E L M O P R S T X                 [ one string per line ]
 *
 *  % more words3.txt
 *  bed bug dad yes zoo ... all bad yet
 *
 *  % java MergeX < words3.txt
 *  all bad bed bug dad ... yes yet zoo    [ one string per line ]
 *
 *************************************************************************/

public class XMergeX {
  private static final int CUTOFF = 7;  // cutoff to insertion sort


  private static <T extends Comparable<? super T>> void merge(T[] src, T[] dst, int lo, int mid, int hi) {

    // precondition: src[lo .. mid] and src[mid+1 .. hi] are sorted subarrays
    assert isSorted(src, lo, mid);
    assert isSorted(src, mid+1, hi);

    int i = lo, j = mid+1;
    for (int k = lo; k <= hi; k++) {
      if      (i > mid)              dst[k] = src[j++];
      else if (j > hi)               dst[k] = src[i++];
      else if (less(src[j], src[i])) dst[k] = src[j++];   // to ensure stability
      else                           dst[k] = src[i++];
    }
    if (COUNT_OPS) DoublingTest.addOps (hi-lo);

    // postcondition: dst[lo .. hi] is sorted subarray
    assert isSorted(dst, lo, hi);
  }

  private static <T extends Comparable<? super T>> void sort(T[] src, T[] dst, int lo, int hi) {
    if (hi <= lo + CUTOFF) {
      insertionSort(src, lo, hi);
      return;
    }
    int mid = lo + (hi - lo) / 2;
    sort(dst, src, lo, mid);
    sort(dst, src, mid+1, hi);

    /*
        if (!less(dst[mid+1], dst[mid])) {
            for (int i = lo; i <= hi; i++) src[i] = dst[i];
            return;
        }
     */
    // a bit faster
    if (!less(dst[mid+1], dst[mid])) {
      System.arraycopy(dst, lo, src, lo, hi - lo + 1);
      return;
    }

    merge(dst, src, lo, mid, hi);
  }

  public static <T extends Comparable<? super T>> void sort(T[] a) {
    /*
        Comparable[] aux = new Comparable[a.length];
        for (int i = 0; i < a.length; i++)
            aux[i] = a[i];
     */
    // a bit faster
    T[] aux = a.clone();
    sort(a, aux, 0, a.length-1);

    assert isSorted(a);
  }


  // 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);
  }


  // 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;
  }

  // is a[i] < a[j]?
  private static <T extends Comparable<? super T>> boolean less(T a, T b) {
    if (COUNT_OPS) DoublingTest.incOps ();
    return (a.compareTo(b) < 0);
  }

  /* *********************************************************************
   *  Check if array is sorted - useful for debugging
   ***********************************************************************/
  private static <T extends Comparable<? super T>> boolean isSorted(T[] a) {
    return isSorted(a, 0, a.length - 1);
  }

  private static <T extends Comparable<? super T>> boolean isSorted(T[] a, int lo, int hi) {
    for (int i = lo + 1; i <= hi; i++)
      if (less(a[i], a[i-1])) 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) {
    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));

  }
}