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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:
0
45, 75, 31, 52, 27
Bob, Nick, Anne, Mary, Larry, Celia
1
2
3
4
5
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
next node
object
Instantiating a LinkedList
• LinkedList<E>
• Examples:
LinkedList<BigInteger> bigLst = new LinkedList<BigInteger>();
LinkedList<String> stringLst = new LinkedList<String>();
LinkedList Functionality
• add(aObject) –
add aObject to end of list
add(new BigInteger(“234512909345689131321122110863523”))
•
•
•
•
•
•
•
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<String> list = new LinkedList<String>();
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 " + "\"" +
System.out.println("last item in list is " + "\"" +
list.getFirst() + "\"");
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.
231-45-3278
229-03-1259
256-41-0920
209-60-8877
keys
Jones, William
Keller, Mary
Madden, Matt
Jones, William
values
HashMap
• Table consisting of two columns
• Column 1 contains the keys
• Column 2 contains the values
Keys
Values
231-45-3278
Jones, William
229-03-1259
Keller, Mary
256-41-0920
Madden, Matt
200-60-8877
Jones, William
Like a one-dimensional array, where a key acts like an index to access the corresponding value
Instantiating a HashMap
• HashMap<K,E>
• Examples:
HashMap<String, String> hmap = new HashMap<String, String>();
HashMap<String, LinkedList<String>> amap =
new HashMap<String, LinkedList<String>>();
HashMap Functionality
• get(aKey) –
returns corresponding value
get(“229-03-1259”) = “Keller, Mary”
• put(aKey, aValue) –
inserts a <key,value> pair
put(“229-03-1259”, “Keller, Mary”)
• containsKey(aKey) –
does key belong
• containsValue(aValue) –
• remove(aKey) –
does value belong
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<String,Double> table = new HashMap<String,Double>();
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"))
if(!table.containsKey("Donna"))
table.put("Al",28.0);
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
sorted
Keys
Values
200-60-8877
Jones, William
229-03-1259
Keller, Mary
231-45-3278
Jones, William
256-41-0920
Madden, Matt
Instantiating a TreeMap
• TreeMap<K,E>
• Examples:
TreeMap<String, String> hmap = new TreeMap<String, String>();
TreeMap<String, Double> amap = new TreeMap<String, Double>();
TreeMap Functionality
• get(aKey) –
returns corresponding value
get(“229-03-1259”) = “Keller, Mary”
• put(aKey, aValue) –
inserts a <key,value> pair
put(“229-03-1259”, “Keller, Mary”)
• containsKey(aKey) –
does key belong
• containsValue(aValue) –
• remove(aKey) –
does value belong
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
231-45-3278
229-03-1259
200-60-8877
Keller, Mary
Jones, William
Jones, William
256-41-0920
Madden, Matt
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