// Helene Martin, CSE 143
// Shows the merge sort algorithm we discussed in an array of ints in a Queue of String.  
// Because Queues have different properties than arrays, the code is a little different 
// but the algorithm is the same.

import java.util.*;

public class QueueSorting {
   // Sorts the given queue using the merge sort algorithm
   // Post: list is in sorted (nondecreasing) order
   public static void sort(Queue<String> list) {
      if (list.size() > 1) {
         Queue<String> left = new LinkedList<String>();
         Queue<String> right = new LinkedList<String>();
         int size1 = list.size() / 2;
         int size2 = list.size() - size1;

         for (int i = 0; i < size1; i++) {
            left.add(list.remove());
         }

         for (int i = 0; i < size2; i++) {
            right.add(list.remove());
         }

         sort(left);
         sort(right);

         mergeInto(list, left, right);
      }
   }

   // Merges list1 and list2 into a result queue.
   // Pre : result is empty; list1 is sorted; list2 is sorted
   // Post: list1 is empty; list2 is empty
   public static void mergeInto(Queue<String> result, Queue<String> list1,
         Queue<String> list2) {
      while (!list1.isEmpty() && !list2.isEmpty()) {
         if (list1.peek().compareTo(list2.peek()) <= 0)
            result.add(list1.remove());
         else
            result.add(list2.remove());
      }

      while (!list1.isEmpty()) {
         result.add(list1.remove());
      }

      while (!list2.isEmpty()) {
         result.add(list2.remove());
      }
   }
}