content: /*************************************************************************
   *  Compilation:  javac Shell.java
   *  Execution:    java Shell < input.txt
   *  Dependencies: StdOut.java StdIn.java
   *  Data files:   http://algs4.cs.princeton.edu/21sort/tiny.txt
   *                http://algs4.cs.princeton.edu/21sort/words3.txt
   *   
   *  Sorts a sequence of strings from standard input using shellsort.
   *
   *  Uses increment sequence proposed by Sedgewick and Incerpi.
   *  The nth element of the sequence is the smallest integer >= 2.5^n
   *  that is relatively prime to all previous terms in the sequence.
   *  For example, incs[4] is 41 because 2.5^4 = 39.0625 and 41 is
   *  the next integer that is relatively prime to 3, 7, and 16.
   *   
   *  % more tiny.txt
   *  S O R T E X A M P L E
   *
   *  % java Shell < tiny.txt
   *  S O R T E X A M P L E A               [ one string per line ]
   *    
   *  % more words3.txt
   *  bed bug dad yes zoo ... all bad yet
   *  
   *  % java Shell < words3.txt
   *  all bad bed bug dad ... yes yet zoo    [ one string per line ]
   *
   *
   *************************************************************************/
  
  public class Shell {
  
      // sort the array a[] in ascending order using Shellsort
      public static void sort(Comparable[] 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 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;
      }
  
      // is the array h-sorted?
      private static boolean isHsorted(Comparable[] 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 void show(Comparable[] a) {
          for (int i = 0; i < a.length; i++) {
              StdOut.println(a[i]);
          }
      }
  
      // Read strings from standard input, sort them, and print.
      public static void main(String[] args) {
          String[] a = StdIn.readStrings();
          Shell.sort(a);
          show(a);
      }
  
  }
  