content: /*************************************************************************
   *  Compilation:  javac Merge.java
   *  Execution:    java Merge < input.txt
   *  Dependencies: StdOut.java StdIn.java
   *  Data files:   http://algs4.cs.princeton.edu/22merge/tiny.txt
   *                http://algs4.cs.princeton.edu/22merge/words3.txt
   *   
   *  Sorts a sequence of strings from standard input using mergesort.
   *   
   *  % more tiny.txt
   *  S O R T E X A M P L E
   *
   *  % java Merge < 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 Merge < words3.txt
   *  all bad bed bug dad ... yes yet zoo    [ one string per line ]
   *  
   *************************************************************************/
  
  public class Merge {
  
      // stably merge a[lo .. mid] with a[mid+1 .. hi] using aux[lo .. hi]
      public static void merge(Comparable[] a, Comparable[] aux, int lo, int mid, int hi) {
  
          // precondition: a[lo .. mid] and a[mid+1 .. hi] are sorted subarrays
          assert isSorted(a, lo, mid);
          assert isSorted(a, mid+1, 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++];
              else if (j > hi)               a[k] = aux[i++];
              else if (less(aux[j], aux[i])) a[k] = aux[j++];
              else                           a[k] = aux[i++];
          }
  
          // postcondition: a[lo .. hi] is sorted
          assert isSorted(a, lo, hi);
      }
  
      // mergesort a[lo..hi] using auxiliary array aux[lo..hi]
      private static void sort(Comparable[] a, Comparable[] aux, int lo, int hi) {
          if (hi <= lo) return;
          int mid = lo + (hi - lo) / 2;
          sort(a, aux, lo, mid);
          sort(a, aux, mid + 1, hi);
          merge(a, aux, lo, mid, hi);
      }
  
      public static void sort(Comparable[] a) {
          Comparable[] aux = new Comparable[a.length];
          sort(a, aux, 0, a.length-1);
          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) {
          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;
      }
  
  
     /***********************************************************************
      *  Index mergesort
      ***********************************************************************/
      // stably merge a[lo .. mid] with a[mid+1 .. hi] using aux[lo .. hi]
      private static void merge(Comparable[] a, int[] index, int[] aux, int lo, int mid, int hi) {
  
          // copy to aux[]
          for (int k = lo; k <= hi; k++) {
              aux[k] = index[k]; 
          }
  
          // merge back to a[]
          int i = lo, j = mid+1;
          for (int k = lo; k <= hi; k++) {
              if      (i > mid)                    index[k] = aux[j++];
              else if (j > hi)                     index[k] = aux[i++];
              else if (less(a[aux[j]], a[aux[i]])) index[k] = aux[j++];
              else                                 index[k] = aux[i++];
          }
      }
  
      // return a permutation that gives the elements in a[] in ascending order
      // do not change the original array a[]
      public static int[] indexSort(Comparable[] a) {
          int N = a.length;
          int[] index = new int[N];
          for (int i = 0; i < N; i++)
              index[i] = i;
  
          int[] aux = new int[N];
          sort(a, index, aux, 0, N-1);
          return index;
      }
  
      // mergesort a[lo..hi] using auxiliary array aux[lo..hi]
      private static void sort(Comparable[] a, int[] index, int[] aux, int lo, int hi) {
          if (hi <= lo) return;
          int mid = lo + (hi - lo) / 2;
          sort(a, index, aux, lo, mid);
          sort(a, index, aux, mid + 1, hi);
          merge(a, index, aux, lo, mid, hi);
      }
  
      // 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();
          Merge.sort(a);
          show(a);
      }
  }
  