/******************************************************************************
 *  Compilation:  javac Quick.java
 *  Execution:    java Quick < input.txt
 *  Dependencies: System.out.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 quicksort.
 *
 *  % more tiny.txt
 *  S O R T E X A M P L E
 *
 *  % java Quick < 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 Quick < words3.txt
 *  all bad bed bug dad ... yes yet zoo    [ one string per line ]
 *
 *
 *  Remark: For a type-safe version that uses static generics, see
 *
 *    http://algs4.cs.princeton.edu/23quicksort/QuickPedantic.java
 *
 ******************************************************************************/
package ca.bc.webarts.widgets;

/**
 *  The <tt>Quick</tt> class provides static methods for sorting an
 *  array and selecting the ith smallest element in an array using quicksort.
 *  <p>
 *  For additional documentation, see <a href="http://algs4.cs.princeton.edu/21elementary">Section 2.1</a> of
 *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
 *
 *  @author Robert Sedgewick
 *  @author Kevin Wayne
 */
public class Quick
{

  // This class should not be instantiated.
  private Quick()
  { }


  /**
   * Rearranges the array in ascending order, using the natural order.
   * @param a the array to be sorted
   */
  public static void sort( Comparable[] a )
  {
    //StdRandom.shuffle( a );
    sort( a, 0, a.length - 1 );
    assert isSorted( a );
  }


  // quicksort the subarray from a[lo] to a[hi]
  private static void sort( Comparable[] a, int lo, int hi )
  {
    if ( hi <= lo )
    {
      return;
    }
    int j = partition( a, lo, hi );
    sort( a, lo, j - 1 );
    sort( a, j + 1, hi );
    assert isSorted( a, lo, hi );
  }


  // partition the subarray a[lo..hi] so that a[lo..j-1] <= a[j] <= a[j+1..hi]
  // and return the index j.
  private static int partition( Comparable[] a, int lo, int hi )
  {
    int i = lo;
    int j = hi + 1;
    Comparable v = a[lo];
    while ( true )
    {

      // find item on lo to swap
      while ( less( a[ ++i], v ) )
      {
        if ( i == hi )
        {
          break;
        }

        // find item on hi to swap
      }
      while ( less( v, a[ --j] ) )
      {
        if ( j == lo )
        {
          break;
        }        // redundant since a[lo] acts as sentinel

        // check if pointers cross
      }
      if ( i >= j )
      {
        break;
      }

      exch( a, i, j );
    }

    // put partitioning item v at a[j]
    exch( a, lo, j );

    // now, a[lo .. j-1] <= a[j] <= a[j+1 .. hi]
    return j;
  }


  /**
   * Rearranges the array so that a[k] contains the kth smallest key;
   * a[0] through a[k-1] are less than (or equal to) a[k]; and
   * a[k+1] through a[N-1] are greater than (or equal to) a[k].
   * @param a the array
   * @param k find the kth smallest
   */
  public static Comparable select( Comparable[] a, int k )
  {
    if ( k < 0 || k >= a.length )
    {
      throw new IndexOutOfBoundsException( "Selected element out of bounds" );
    }
    //StdRandom.shuffle( a );
    int lo = 0, hi = a.length - 1;
    while ( hi > lo )
    {
      int i = partition( a, lo, hi );
      if ( i > k )
      {
        hi = i - 1;
      }
      else if ( i < k )
      {
        lo = i + 1;
      }
      else
      {
        return a[i];
      }
    }
    return a[lo];
  }


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

  // is v < w ?
  private static boolean less( Comparable v, Comparable 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 boolean isSorted( Comparable[] a )
  {
    return isSorted( a, 0, a.length - 1 );
  }


  private static boolean isSorted( Comparable[] 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 void show( Comparable[] a )
  {
    for ( int i = 0; i < a.length; i++ )
    {
      System.out.println( a[i] );
    }
  }


  /**
   * Reads in a sequence of strings from standard input; quicksorts them;
   * and prints them to standard output in ascending order.
   * Shuffles the array and then prints the strings again to
   * standard output, but this time, using the select method.
   */
  public static void main( String[] args )
  {
    String[] a = args;// StdIn.readAllStrings();
    Quick.sort( a );
    show( a );

    // shuffle
   // StdRandom.shuffle( a );

    // display results again using select
    System.out.println();
    for ( int i = 0; i < a.length; i++ )
    {
      String ith = ( String ) Quick.select( a, i );
      System.out.println( ith );
    }
  }

}