Question: Priority Queue "deleteMin()" trouble

Question

Hello, I am having trouble formulating a delete() method here, which could also be called deleteMin() here.
The priority queue, is suppose to have quick insertion O(1) time, and slow deletion O(N) because it's going to have to search through the unordered array, find the minimum object then delete it once "delete()" is called.
However, I am stuck on trying to come up with the logic for my delete() method....
Here's what I am thinking...
I need to examine all the items and shift half of them, on average, down to fill in the hole once the minimum item is found.
How would I find the minimum item, and once found how would I delete this? Any direction or statements you can show me to clear this up would be appreciated. Please see my code below :) Please excuse my empty javadocs as of right now, I do those last.
Thank you
* This class is to demonstrate.....
* @version 1.0
public class PriorityQ {
     private int maxSize;
     private long[] queArray;
     private int nItems;
      * Javadoc here
     public PriorityQ(int s) // constructor
          maxSize = s;
          queArray = new long[maxSize];
          nItems = 0;
      * Javadoc here
     public void insert(long value) {
          queArray[nItems] = value;
          nItems++;
      * Javadoc here
      public long remove () {
      * Javadoc here
     public long peekMin() {
               return queArray[nItems - 1];
      * Javadoc here
     public boolean isEmpty() {
               return (nItems == 0);
      * Javadoc here
     public boolean isFull() {
               return (nItems == maxSize);
} // end class PriorityQ
class PriorityQApp {
             public static void main(String[] args)
                PriorityQ q1 = new PriorityQ(5);
                q1.insert(30);
                q1.insert(50);
                q1.insert(10);
                q1.insert(40);
                while( !q1.isEmpty() )
                   long item = q1.remove();
                   System.out.print(item + " ");  // 10, 20, 30, 40, 50
                   }  // end while
                System.out.println("");
     } // end main()
} // end class PriorityQApp
// //////////////////////////////////////////////////////////////Edited by: Cole1988 on Feb 21, 2009 9:03 AM

Answer 1

Sorry no one got to you sooner.
Using your instance variables:
public long remove()
     long minValue = Long.MAX_VALUE;
     int minIndex = 0;
     for(int i = 0; i < nItems; i++) //Here we iterate through all the items to find the smallest one
          if(queArray[i] < minValue) //If this particular value is less than the smallest one found so far,
               minValue = queArray; //This value is now the smallest one found so far
               minIndex = i; //minIndex now contains the index of the smallest one found so far
     /*Now we can remove the smallest term, because after the above iteration, minIndex is the index number of the smallest value and minValue is the smallest value.*/
     for(int i = minIndex + 1; i < nItems; i++) //Starting at the term right AFTER the smallest one
          queArray[i-1]=queArray[i]; //Copy the value into the space right BEFORE it
     nItems--; //The number of items has decreased by one
     return minValue;
}Note: This code does NOT resize your array after you remove an item; depending on how you'll implement it, you'll need to check if you're about to overflow the array by comparing nItems with queArray.length and resize your array accordingly.
It seems like you're a bit confused about loops and iterating through arrays; I'd recommend reviewing a good Java book or online tutorial and practicing with some basic array iterations before you go any farther. You've got the basic grasp of things, it just hasn't "clicked" for you yet. :)
Let me know if you need any more help or if you don't understand anything about what I just said.
Regards,
Alvin