content: /*************************************************************************
   *  Compilation:  javac Quick3way.java
   *  Execution:    java Quick3way < 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 3-way quicksort.
   *   
   *  % more tiny.txt
   *  S O R T E X A M P L E
   *
   *  % java Quick3way < 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 Quick3way < words3.txt
   *  all bad bed bug dad ... yes yet zoo    [ one string per line ]
   *
   *************************************************************************/
  
  public class Quick3way {
  
      // quicksort the array a[] using 3-way partitioning
      public static void sort(Comparable[] a) {
          sort(a, 0, a.length - 1);
          assert isSorted(a);
      }
  
      // quicksort the subarray a[lo .. hi] using 3-way partitioning
      private static void sort(Comparable[] a, int lo, int hi) { 
          if (hi <= lo) return;
          int lt = lo, gt = hi;
          Comparable v = a[lo];
          int i = lo;
          while (i <= gt) {
              int cmp = a[i].compareTo(v);
              if      (cmp < 0) exch(a, lt++, i++);
              else if (cmp > 0) exch(a, i, gt--);
              else              i++;
          }
  
          // a[lo..lt-1] < v = a[lt..gt] < a[gt+1..hi]. 
          sort(a, lo, lt-1);
          sort(a, gt+1, hi);
          assert isSorted(a, lo, hi);
      }
  
  
  
     /***********************************************************************
      *  Helper sorting functions
      ***********************************************************************/
      
      // is v < w ?
      private static boolean less(Comparable v, Comparable w) {
          return (v.compareTo(w) < 0);
      }
  
      // does v == w ?
      private static boolean eq(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++) {
              StdOut.println(a[i]);
          }
      }
  
      // Read strings from standard input, sort them, and print.
      public static void main(String[] args) {
          String[] a = StdIn.readStrings();
          Quick3way.sort(a);
          show(a);
      }
  
  }
  