content: /*************************************************************************
   *  Compilation:  javac Quick.java
   *  Execution:    java Quick < 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 quicksort.
   *   
   *  % more tiny.txt
   *  S O R T E X A M P L E
   *
   *  % java Quick < 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 Quick < words3.txt
   *  all bad bed bug dad ... yes yet zoo    [ one string per line ]
   *
   *************************************************************************/
  
  public class Quick {
  
      // quicksort the array
      public static void sort(Comparable[] a) {
          StdRandom.shuffle(a);
          sort(a, 0, a.length - 1);
      }
  
      // 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] by returning an index j
      // so that a[lo .. j-1] <= a[j] <= a[j+1 .. hi]
      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 v = a[j] into position
          exch(a, lo, j);
  
          // with a[lo .. j-1] <= a[j] <= a[j+1 .. hi]
          return j;
      }
  
     /***********************************************************************
      *  Rearranges the elements in a so that a[k] is the kth smallest element,
      *  and 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].
      ***********************************************************************/
      public static Comparable select(Comparable[] a, int k) {
          if (k < 0 || k >= a.length) {
              throw new RuntimeException("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++) {
              StdOut.println(a[i]);
          }
      }
  
      // Read strings from standard input, sort them, and print.
      public static void main(String[] args) {
          String[] a = StdIn.readStrings();
          Quick.sort(a);
          show(a);
  
          // display results again using select
          StdOut.println();
          for (int i = 0; i < a.length; i++) {
              String ith = (String) Quick.select(a, i);
              StdOut.println(ith);
          }
      }
  
  }
  