package algorithms.mergesort22;

 import algorithms.util.StdIn;

 import algorithms.util.StdOut;

 /******************************************************************************

  *  Compilation:  javac MergeBU.java

  *  Execution:    java MergeBU < input.txt

  *  Dependencies: StdOut.java StdIn.java

  *  Data files:   http://algs4.cs.princeton.edu/22mergesort/tiny.txt

  *                http://algs4.cs.princeton.edu/22mergesort/words3.txt

  *

  *  Sorts a sequence of strings from standard input using

  *  bottom-up mergesort.

  *

  *  % more tiny.txt

  *  S O R T E X A M P L E

  *

  *  % java MergeBU < 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 MergeBU < words3.txt

  *  all bad bed bug dad ... yes yet zoo    [ one string per line ]

  *

  ******************************************************************************/

 /**

  *  The <tt>MergeBU</tt> class provides static methods for sorting an

  *  array using bottom-up mergesort.

  *  <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 MergeBU {

     // This class should not be instantiated.

     private MergeBU() { }

     // stably merge a[lo..mid] with a[mid+1..hi] using aux[lo..hi]

     private static void merge(Comparable[] a, Comparable[] aux, int lo, int mid, int hi) {

         // copy to aux[]

         for (int k = lo; k <= hi; k++) {

             aux[k] = a[k];

         }

         // merge back to a[]

         int i = lo, j = mid+1;

         for (int k = lo; k <= hi; k++) {

             if      (i > mid)              a[k] = aux[j++];  // this copying is unneccessary

             else if (j > hi)               a[k] = aux[i++];

             else if (less(aux[j], aux[i])) a[k] = aux[j++];

             else                           a[k] = aux[i++];

         }

     }

     /**

      * Rearranges the array in ascending order, using the natural order.

      * @param a the array to be sorted

      */

     public static void sort(Comparable[] a) {

         int N = a.length;

         Comparable[] aux = new Comparable[N];

         for (int n = 1; n < N; n = n+n) {

             for (int i = 0; i < N-n; i += n+n) {

                 int lo = i;

                 int m  = i+n-1;

                 int hi = Math.min(i+n+n-1, N-1);

                 merge(a, aux, lo, m, hi);

             }

         }

         assert isSorted(a);

     }

   /***********************************************************************

     *  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) {

         for (int i = 1; i < a.length; 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++) {

             StdOut.println(a[i]);

         }

     }

     /**

      * Reads in a sequence of strings from standard input; bottom-up

      * mergesorts them; and prints them to standard output in ascending order.

      */

     public static void main(String[] args) {

         String[] a = StdIn.readAllStrings();

         MergeBU.sort(a);

         show(a);

     }

 }