Added Queues, Priority Queues and Linked Lists

data_structures/LinkedLists.java

@@ -0,0 +1,69 @@
+/*
+ * A linked list is similar to an array, it holds values. However, links in a linked list do not have indexes.
+ * With a linked list you do not need to predetermine it's size as it grows and shrinks as it is edited.
+ * This is an example of a singly linked list. Elements can only be added/removed at the head/front of the list.
+*/
+class LinkedList{
+	private Link head; //Head refers to the front of the list
+
+	public LinkedList(){
+		head = null;
+	}
+
+	public void insertHead(int x){	//Insert an element at the head
+		Link newLink = new Link(x); //Create a new link with a value attached to it
+		newLink.next = head; 		//Set the new link to point to the current head
+		head = newLink; 			//Now set the new link to be the head
+	}
+
+	public Link deleteHead(){ //Delete the element at the head
+		Link temp = head;
+		head = head.next; //Make the second element in the list the new head, the Java garbage collector will later remove the old head
+		return temp;
+	}
+
+	public boolean isEmpty(){ //Returns true if list is empty
+		return(head == null);
+	}
+
+	public void display(){ //Prints contents of the list
+		Link current = head;
+		while(current!=null){
+			current.displayLink();
+			current = current.next;
+		}
+		System.out.println();
+	}
+}
+
+class Link{
+	public int value;
+	public Link next; //This is what the link will point to
+
+	public Link(int valuein){
+		value = valuein;
+	}
+
+	public void displayLink(){
+		System.out.print(value+" ");
+	}
+}
+
+//Example
+public class LinkedLists{
+	public static void main(String args[]){
+		LinkedList myList = new LinkedList();
+
+		System.out.println(myList.isEmpty()); //Will print true
+
+		myList.insertHead(5);
+		myList.insertHead(7);
+		myList.insertHead(10);
+
+		myList.display(); // 10(head) --> 7 --> 5
+
+		myList.deleteHead();
+
+		myList.display(); // 7(head) --> 5
+	}
+}

data_structures/PriorityQueues.java

@@ -22,10 +22,10 @@ class PriorityQueue{
 		else{
 			int j = nItems;
 			while(j > 0 && queueArray[j-1] > value){
-				queueArray[j] = queueArray[j-1];
+				queueArray[j] = queueArray[j-1]; //Shifts every element up to make room for insertion
 				j--;
 			}
-			queueArray[j] = value;
+			queueArray[j] = value; //Once the correct position is found the value is inserted
 		}
 		nItems++;
 	}