package algs23;
import stdlib.*;
/* ***********************************************************************
 *  Compilation:  javac QuickDualPivot.java
 *  Execution:    java QuickDualPivot < input.txt
 *  Dependencies: StdOut.java StdIn.java
 *  Data files:   http://algs4.cs.princeton.edu/23quicksort/tiny.txt
 *                http://algs4.cs.princeton.edu/23quicksort/words3.txt
 *
 *  Sorts a sequence of strings from standard input using dual-pivot
 *  quicksort.
 *
 *  [Warning: not thoroughly tested.]
 *
 *  % more tiny.txt
 *  S O R T E X A M P L E
 *
 *  % java QuickDualPivot < 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 QuickDualPivot < words3.txt
 *  all bad bed bug dad ... yes yet zoo    [ one string per line ]
 *
 *************************************************************************/

public class XQuickDualPivot {

  // quicksort the array a[] using dual-pivot quicksort
  public static <T extends Comparable<? super T>> void sort(T[] a) {
    sort(a, 0, a.length - 1);
    assert isSorted(a);
  }

  // quicksort the subarray a[lo .. hi] using dual-pivot quicksort
  private static <T extends Comparable<? super T>> void sort(T[] a, int lo, int hi) {
    if (hi <= lo) return;

    // make sure a[lo] <= a[hi]
    if (less(a[hi], a[lo])) exch(a, lo, hi);

    int lt = lo + 1, gt = hi - 1;
    int i = lo + 1;
    while (i <= gt) {
      if       (less(a[i], a[lo])) exch(a, lt++, i++);
      else if  (less(a[hi], a[i])) exch(a, i, gt--);
      else                         i++;
    }
    exch(a, lo, --lt);
    exch(a, hi, ++gt);

    // recursively sort three subarrays
    sort(a, lo, lt-1);
    if (less(a[lt], a[gt])) sort (a, lt+1, gt-1);
    sort(a, gt+1, hi);

    assert isSorted(a, lo, hi);
  }



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

  // is v < w ?
  private static <T extends Comparable<? super T>> boolean less(T v, T w) {
    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) {
    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);
    }
  }

  // Read strings from standard input, sort them, and print.
  public static void main(String[] args) {
    String[] a = StdIn.readAllStrings();
    sort(a);
    show(a);
  }

}