1. CSE 214 – Computer Science II Maps
Source:

2. Maps An abstract data structure for storing (key, value) data pairs
called (name, value) on Web
maps may also be called dictionaries, associative arrays, etc.
What’s a key?
a unique identifier for accessing a piece of data
like an ID
What’s a value?
the data

3. You have already built a type of map
PresidentsBST is a Map
Each president has a unique ID
president number
ID provides a natural sorting/ordering
Only difference:
we didn’t call it a map
we didn’t adhere to a specific map interface

4. Game Programmers Love Maps
Why?
To store commonly used assets
Example: 3D Model of a dragon
suppose we need to render 3 or more identical dragons
same geometry, same textures, same animations, etc.

5. What do we do? Construct Dragon object for each one Instead:
will keep track of location, animation state, damage, etc.
don’t load dragon artwork 3 times
Instead:
load dragon artwork once
store it in a dictionary (map)
Optimized for fast access (log N)
give map key of dragon to all Dragon objects
At render time:
retrieve 3D dragon model from dictionary using ID
render the 3 models

6. The java.util.Map interface
Map methods:
V get(K key, V value)
V put(K key, V value)
V remove(Object key)
Colletions<V> values() – to help with getting an Iterator
Manages Map.Entry objects

7. The java.util.Map.Entry Interface
A Map.Entry has:
2 variables
Object: key
Object: value
accessors for getting key & value
mutator for setting value

8. Ex: HashMap vs. TreeMap Both are maps Both classes implement Map
both have the same methods
Underlying data structures are different
HashMap is a hash table
TreeMap is a red-black tree
a self-balancing binary search tree

9. So what are we using maps for?
Storing our Airports
a lookup dictionary
Why?
because we have a lot of data
fast way of getting this info

10. Our updated AirportGraph
public class AirportGraph { // THESE ARE THE NODES IN THE GRAPH public TreeMap<String,Airport> vertices = new TreeMap<String,Airport>(); // THESE ARE THE CONNECTIONS BETWEEN THE NODES // FOR EACH AIRPORT CODE, WE HAVE A SORTED Vector // OF THE ADJACENT AIRPORT CODES public TreeMap<String,Vector<String>> edges = new TreeMap<String,Vector<String>>();

11. How might we find a shortest path?
This is a bonus part of the assignment
We can do this by remembering shortest paths to other nodes
Let’s do another example

12. Depth First Search vs. Breadth First Search
Again, let’s do an example