Thread: Creating methods in a singly linked list?

I want to create 4 methods for my singly linked list class: public boolean removeFirstOccurence(Object o), public boolean removeLastOccurence(Object o), public int indexOf(Object o), public int lastIndexOf(Object o). I am confused about having an Object as a parameter. Therefore I don't have any idea how to write these methods. I'm not gonna ask you to write it for me but can anyone sort of give me the skeleton code of each method so I can understand what is going on? I'm desperate!

You give us the skeleton code, and we'll help you make it better.

You say you're confused about having Object as a parameter, so what parameter would you not be confused about? Write the methods with the less confusing parameter first, and then we can help you change them to use Object as a parameter.

Okay well I did a little research and I think I've created the first two methods roughly. So lets start with the first two. Here is my code:

		 public E remove(int index) {
			 Node<E> temp = head;
			   assert(index >= 0 && index < size); //force valid index  
			   temp = head; //start at the beginning of the list  
			   if(index == 0){  
				   E result = head.data;  
				   head = head.next;   
				   size--;  
				   return result;  
			   }  
			   else if(index == size){  
				   E result = tail.data;  
				   tail = getNode(size-2);  
				   size--;  
				   return result;  
			   }  
			  //iterate to the position before the index  
			   for(int i = 0; i < index-1; i++) temp = temp.next;  
			   Node<E> current = temp.next;  
			   //set temp.next to point to the Node next to the Node to be removed  
			   temp.next = current.next;   
			   E result = current.data; //store the element to return  
			   current = null; //remove the node  
			   size--; //decrement size  
			   return result; //return the element at that position  
		 }
 
		 public boolean removeFirstOccurence(Object o) {
			 Node<E> temp = head;
			 if(this == head.data) {
				 head = head.next;
				 size--;
				 return true;
			 }
			 else if(this == tail.data) {
				 tail = getNode(size-2);
				 size--;
				 return true;
			 }
			 for(int i = 1; i < size-2; i++) temp = temp.next;
			 	if(this.equals(getNode(i))) {
			 		temp = null;
                                                                      size--;
			 		return true;
			 	}
			return false;
		 }

So I think the first method should work correctly... however for the second I'm getting an error at the if statement within the for loop. How can I fix this?

Also, the next method I have to write is removeLastOccurence(Object o), and I'm not sure how to go about that. How do you tell the compiler to skip the first occurrence and each subsequent until you get to the last one? What if there is no second occurrence? Would the last occurrence then be the first one?

So for the error, it tells me "i cannot be resolved to a variable."

Perhaps you didn't understand my question. For the removeLastOccurence method, the program needs to skip over the first and subsequent occurrences of an object until it gets to the last occurrence, and then delete the last one. I was wondering how to write a method to do that. For removeFirstOccurence you don't need to worry about each subsequent occurrence, just delete the first that is found. But this one you do need to worry about them.

Right, it shows the error at the "i" in the line if(this.equals(getNode(i))). I'm trying to compare the argument to the node at index i. Could you show me how I can do this properly to correct the method so that it executes properly?

I'm sorry, I used the wrong word.

The question you are asking me is the question I'm having trouble answering.

Great, it worked, thank you.

Well to find the suit of that last queen... every deck of cards should only have 4 queens, so you just look for the 4th queen and return the suit. So does this mean you should know how many of each occurrence there is in a linked list?

So then if you go through the deck of cards and look at each card one by one, you wouldn't know which is the last one until you go through the whole deck. Would you then have to go through the deck again to locate the last queen now that you know which one it is?

Perhaps... depending on how big the deck of cards is. So to write this method I would start off with a loop that compares the data to the argument... and then what?