LinkedLists CS445 Data Structures

What is a list? A list is an object that is a sequence of objects. The positions in the list are numbered 0, 1, 2, … or may be numbered 1, 2, 3, … Examples: 45, 75, 31, 52, 27 Bob, Nick, Anne, Mary, Larry, Celia

LinkedList of Chairs

LinkedList Head

What is a LinkedList? A LinkedList is one of the many ways to implement a list Each object is stored in a node of the form object next node

Instantiating a LinkedList LinkedList Examples: LinkedList bigLst = new LinkedList (); LinkedList stringLst = new LinkedList ();

LinkedList Functionality add(aObject) – add aObject to end of list add(new BigInteger( )) add(aObject, position) – add aObject at the position size() – size of list contains(aObject) – does aObject belong to list get(position) – get object at position in list remove() – remove object at beginning of list remove(position) – remove object from position indexOf(aObject) - remove object at position

LinkedList list = new LinkedList (); list.add("Bob"); list.add("Al"); list.add("Carl"); list.add(1,"Sela"); list.add(0,"Morgan"); list.add(3,"Mona"); System.out.println("list = " + list); System.out.println("size = " + list.size() ); if( list.contains("Mona " ) ){ list.remove(list.indexOf("Mona")); System.out.println("deleting " + "\"Mona\""); } System.out.println("list = " + list); System.out.println("first item in list is " + "\"" + list.getFirst() + "\""); System.out.println("last item in list is " + "\"" + list.getLast() + "\"");

Maps

What is a Map? An object that maps keys to values A map cannot contain duplicate keys A map may contain duplicate values Each key can map to at most one value. keys values Jones, William Keller, Mary Madden, Matt Jones, William

HashMap Table consisting of two columns Column 1 contains the keys Column 2 contains the values Jones, William Keller, Mary Madden, Matt Jones, William KeysValues Like a one-dimensional array, where a key acts like an index to access the corresponding value

Instantiating a HashMap HashMap Examples: HashMap hmap = new HashMap (); HashMap > amap = new HashMap >();

HashMap Functionality get(aKey) – returns corresponding value get( ) = Keller, Mary put(aKey, aValue) – inserts a pair put( , Keller, Mary) containsKey(aKey) – does key belong containsValue(aValue) – does value belong remove(aKey) – remove a pair whose key is aKey

HashMap Class values() – returns the set of all values keySet() - returns the set of all keys A HashMap is an implementation of a data structure called a hash table

import java.util.*; public class testHashMap{ public static void main(String[] args){ HashMap table = new HashMap (); table.put("Bob",28.0); table.put("Al",28.0); table.put("Carl",38.0); System.out.println(table.get("Al")); System.out.println(table.get("Carl")); if(!table.containsKey("Al")) table.put("Al",28.0); if(!table.containsKey("Donna")) table.put("Donna",24.0); System.out.println(table.keySet()); System.out.println(table.values()); }

TreeMap Sorted table with respect to keys Column 1 contains the keys Column 2 contains the values Jones, William Keller, Mary Jones, William Madden, Matt KeysValues sorted

Instantiating a TreeMap TreeMap Examples: TreeMap hmap = new TreeMap (); TreeMap amap = new TreeMap ();

TreeMap Functionality get(aKey) – returns corresponding value get( ) = Keller, Mary put(aKey, aValue) – inserts a pair put( , Keller, Mary) containsKey(aKey) – does key belong containsValue(aValue) – does value belong remove(aKey) – remove a pair whose key is aKey

TreeMap Class values() – returns the set of all values keySet() - returns the set of all keys

TreeMap as a Tree A TreeMap is an implementation of a data structure called a binary search tree Jones, William Keller, Mary Madden, Matt Jones, William