priorityQ.java

// priorityQ.java
// demonstrates priority queue
// to run this program: C>java PriorityQApp
////////////////////////////////////////////////////////////////
class PriorityQ
   {
   // array in sorted order, from max at 0 to min at size-1
   private int maxSize;
   private long[] queArray;
   private int nItems;
//-------------------------------------------------------------
   public PriorityQ(int s)          // constructor
      {
      maxSize = s;
      queArray = new long[maxSize];
      nItems = 0;
      }
//-------------------------------------------------------------
   public void insert(long item)    // insert item
      {
      int j;

      if(nItems==0)                         // if no items,
         queArray[nItems++] = item;         // insert at 0
      else                                // if items,
         {
         for(j=nItems-1; j>=0; j--)         // start at end,
            {
            if( item > queArray[j] )      // if new item larger,
               queArray[j+1] = queArray[j]; // shift upward
            else                          // if smaller,
               break;                     // done shifting
            }  // end for
         queArray[j+1] = item;            // insert it
         nItems++;
         }  // end else (nItems > 0)
      }  // end insert()
//-------------------------------------------------------------
   public long remove()             // remove minimum item
      { return queArray[--nItems]; }
//-------------------------------------------------------------
   public long peekMin()            // peek at minimum item
      { return queArray[nItems-1]; }
//-------------------------------------------------------------
   public boolean isEmpty()         // true if queue is empty
      { return (nItems==0); }
//-------------------------------------------------------------
   public boolean isFull()          // true if queue is full
      { return (nItems == maxSize); }
//-------------------------------------------------------------
   }  // end class PriorityQ
////////////////////////////////////////////////////////////////
class PriorityQApp
   {
   public static void main(String[] args)
      {
      PriorityQ thePQ = new PriorityQ(5);
      thePQ.insert(30);
      thePQ.insert(50);
      thePQ.insert(10);
      thePQ.insert(40);
      thePQ.insert(20);

      while( !thePQ.isEmpty() )
         {
         long item = thePQ.remove();
         System.out.print(item + " ");  // 10, 20, 30, 40, 50
         }  // end while
      System.out.println("");
      }  // end main()
//-------------------------------------------------------------
   }  // end class PriorityQApp
////////////////////////////////////////////////////////////////