3503 COP Computer Science II CLASS NOTES - DAY #20 Linked Lists Chapter 16
General Characteristics Allow general access (i.e., not constrained to the beginning or end of the list as with a stack or a queue). Consists of dynamically allocated nodes (containing both a data section and a reference section) that are connected together. Singly Linked List Each node contains a reference to the next node in the list. The last node in the list contains a reference to null, indicating that it is the last node in the list. Movement through the list is uni-directional, i.e., one-way. A head Recall that the basic operations that are needed on a linked list are: insert, delete, and find at the minimum, but helper operations are extremely useful. Java Implementation //definition of a node class public class Node { public Object data; public Node next; private Node ( ) { } //defeats improper instantiation public Node (Object x) //constructor for Node alpha = new Node (x); { data = x; null x next = null; } //end constructor public Node (Object x, Node n) //for Node beta = new Node (x, alpha); { data = x; next = n; x } //end constructor } //end class Node n
Day 20 - 1
B
C
null
Single Linked List Implementation in Java public class Singly_Linked_List { private Node header; private Node current; public Singly_Linked_List ( ) { header = new Node(null, null); gotoHeader ( ); } // end constructor // NOTE: header eliminates the special case for insertion as // now all nodes have at least one node in front of them. public void resetList ( ) { header.next = null; } //end resetList public boolean isEmpty ( ) { return (header.next = = null); } // end isEmpty public void gotoHeader ( ) { current = header; } //end gotoHeader public void gotoFirst ( ) { current = header.next; } //end gotoFirst public void walkForward ( ) { current = current.next; // } end walkForward public void insert (Object x) // new node inserted between current and current.next { if (current = = null) System.out.println(ERROR); else { Node newN = new Node( x, current.next); current.next = newN; current = newN; } // end if-else } // end insert
Day 20 - 2
public void remove (Node n) //removes the node after node n in the list { if (current = = null) System.out.println(ERROR); else { Node temp = current.next; n.next = temp; current = n; } // end if-else } // end remove public Node find (Object x) { Node finder = header; Node temp = header; while (finder.next != null && !finder.next.data.equals (x)) { temp = finder; finder = finder.next; } current = finder.next; return temp.next; } // end find public Node get (Object x) { Node n = find (x); // assume the user does something like the following after doing a find (x) // if (current = = null) // { current = n; // System.out.print(x + Not Found); // } return current; } // end get } // end Singly_Linked_List
Day 20 - 3
Details Of How It Works Shown below is a diagram of how insert works: list before insert: A current list after insert: A D D
current
E
newN Shown below is a diagram of how remove works: list before remove: A B current list after remove: A current B C temp D C temp D
Day 20 - 4
Shown below are diagrams which illustrate how find works: Assume this initial list for all cases: null header Case #1: find (B) null header finder temp null header temp A finder B current C A B C null A B current C null
Note: Reference to node containing A is returned Case #2: find (D) null header temp finder null header temp A B C
A finder
B
C
Day 20 - 5
null header
A temp
B finder
C
null header
A
B temp
C finder
At this point finder.next = null so the loop ends and a reference to the node containing C is returned (temp.next)
Day 20 - 6