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Linked Lists
CSC 172
SPRING 2002
LECTURE 3
Data Structures?
We make distinctions in the level of abstractionAbstract Data Type (ADT) - functionality/behavior
Dictionary, Stack, Queue
Data Model – organizationList, Tree, Graph
Data Structure – implementationArray, Linked list, BST, Adjacency Matrix
The Dictionary ADT Computer programs commonly maintain a set of
values where we wish to Insert elements into the setDelete Elements from the setLook up elements (see if they are currently in the set)
There are lots of ways to implement this Some are more efficient than others
The Dictionary Interface
public interface Dictionary {
public abstract void insert(Object o);
public abstract void delete(Object o);
public abstract boolean lookup(Object o);
}
List Data Model A list is a finite sequence of zero or more elements
Grocery listLaundry list (a1,a2,…,an)
Formally, we can think of a list as either Empty, orAn element followed by a (possibly empty) list
Lists Empty (no elements) An element (head), followed by a list (tail)
Head sometimes called CARTail sometimes called CDR
Length of a list is 0 for an empty list1 + length(tail) for a non-empty list
How can we implement this?
We can implement a Dictionary ADT . . .
using a list data model . . .
with an array data structure . . .
or a linked-list data structure.
Arrays An array is a collection of data items of the same type Every element of the collection can be accessed
separately.
Object [] data = new Object[10];
Array Implementationpublic class myInfo implements Dictionary{
private int defaultCapacity = 100, length = 0;private Object[] datum;public myInfo() {
datum = new Object[defaultCapacity];} public myInfo(int initCapacity) {
datum = new Object[initCapacity];}
Implementationpublic class myInfo implements Dictionary{
private int defaultCapacity = 100, length = 0;private Object[] datum;public myInfo() {
datum = new Object[defaultCapacity];} public myInfo(int initCapacity) {
datum = new Object[initCapacity];}
Insert
Is this ok?
public void insert (Object o) {
datum[length++] = o;
}
What is the run time?
What if I have more than 100 elements?
Expand
private void expand(){Object[] tempData =
new Object[datum.length * 2];for (int j = 0 ; j<length;j++)
tempData[j] = datum[j];datum = tempData;
}So, what is the runtime of this
InsertBetter?
public void insert (Object o) {
if (length >= (datum.length –1)) expand();
datum[length++] = o;
}
This is what the Java class Vector gets you
What is the (worst case) run time, now?
Self-referential data typesclass Node {
private Object data; // the “data”
private Node next; // the “link”
}
data next
Linked List
A linked list “has-a” reference to a node The “head” of the listThe ending node has “null” for the next
data next data Next
head
data Next
null
Linked-List Implementation
public class myInfo implements Dictionary{
private int length = 0;
private Node head = null;
Adding a first node
Adding a first node
public void insert(Object obj){
Node newLink = new Node();
newLink.data = obj;
newLink.next = head;
head = newLink;
}
What is the run time of this?
Lookup: Array
public boolean lookup(Object o){
for (int j = 0 ; j < length;j++)
if (datum[j].equals(o)) return true;
return false;
}
Run time?
Lookup: Linked List
public boolean lookup(Object o){Object temp = head; while (temp != null){
if ((temp.data).equals(o)) return true;temp = temp.next;
}return false;
}
Run time?
Lookup: Linked List, recursive
public boolean lookup(Object o){return lookupNode(o,head);
}public boolean lookupNode(Object o, Node n){
if (n == null) return false;else if((n.data).equals(o) return true;
else return lookupNode(o,n.next);}
Run time?
Deleting a node from a List
Delete: Linked List, recursive
public boolean delete(Object o){
return deleteNode(o,head);
}
Delete: Linked List, recursive
public void deleteNode(Object o, Node n){if (n == null) return ; if (n.next == null) return;else if(((n.next).data).equals(o)) {
n.next = (n.next).nextreturn ;}else return deleteNode(o,n.next);
} Run time?
Delete: Array
We have to look it up O(n) Deletion is setting it to null But, we have to “shift” all the remaining elements.
Delete: Array
public void delete(Object o){for (int j = 0 ; j < length;j++)
if (datum[j].equals(o)) {for (int k = j; k<(length-1);k++)
datum[k] = datum[k+1];return;
};}Run time?
Compare (worst case) Run Time (what about space?)
ARRAY LINKED-LIST
Insert N (in case of expansion)
1
Lookup N N
Delete N (lookup + shift) N (for lookup)
Workshop sing-up
. The coefficient for the workshop differential is positive and significant. On average, each additional workshop attended in CSC 172 increases the final grade point by 0.19. In substantive terms, this means that a student who attends five additional workshops in CSC 172 should expect his/her grade to increase by almost one full letter grade.
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