CS 340 Homework Alternative 6. Due 11:59 PM Wednesday December 12

Transcription

1 CS 340 Homework Alternative 6 Due 11:59 PM Wednesday December 12

2 Alternative Homework 6 Implement the Dijkstra class and the BinaryHeap class shown on the following slide. The Dijkstra class already includes main that reads a description of the graph from a file and creates the graph. The Dijkstra class has a few differences with the original homework 6 Dijkstra class because it uses the BinaryHeap with decreasekey method for your priority queue The name of the file that creates the graph will be given as a command line argument.

3 Input File The input file includes the number of nodes in the graph and the identity of the source node followed by the edges. The node names will be integers greater than or equal to 0 There is one edge per line The format of an edge is node1 node2 weight

4 Example Input File

5 Undirected Graph (without weights) B 2 C D A 9 F G 7 3 E 2 H 2

6 Adjacency List Undirected Graph (without weights) A A B A F A G B B C B F C C D C F D D E D F E E H F F G F H G G H H

7 Dijkstra.java import java.io.*; import java.util.*; public class Dijkstra { private class Vertex { private EdgeNode edges1; private EdgeNode edges2; private boolean known; private int distance; private int previous; private Vertex() { edges1 = null; edges2 = null; known = false; distance = Integer.MAX_VALUE; previous = -1;

8 Dijkstra.java private class EdgeNode { private int vertex1; private int vertex2; private EdgeNode next1; private EdgeNode next2; private int weight; private EdgeNode(int v1, int v2, EdgeNode e1, EdgeNode e2, int w) { //PRE: v1 < v2 vertex1 = v1; vertex2 = v2; next1 = e1; next2 = e2; weight = w; private Vertex[] g; public Dijkstra(int size) {

9 Dijkstra.java public void addedge(int v1, int v2, int w) { //PRE: v1 and v2 are legitimate vertices //(i.e. 0 <= v1 < g.length and 0 <= v2 < g.length public void printroutes(int j) { //find and print the best routes from j to all other nodes in the graph BinaryHeap p = new BinaryHeap(g.length);

10 Dijkstra.java public static void main(string args[]) throws IOException { BufferedReader b = new BufferedReader(new FileReader(args[0])); String line = b.readline(); int numnodes = new Integer(line); line = b.readline(); int source = new Integer(line); System.out.println(source); Dijkstra g = new Dijkstra(numNodes); line = b.readline(); while (line!= null) { Scanner scan = new Scanner(line); g.addedge(scan.nextint(), scan.nextint(), scan.nextint()); line = b.readline(); g.printroutes(source);

11 Binary Heap public class BinaryHeap { //implements a binary heap of where the heap rule is the value in the parent node is less than //or equal to the values in the child nodes private class Item implements Comparable { private int node; private int distance; //the priority private Item(int n, int d) { node = n; distance = d; public int compareto(object z) { return distance - ((Item) z).distance;

12 Binary Heap private Item items[]; private int locations[]; private int size; public BinaryHeap(int s) { items = new Item[s+1]; locations = new int[s]; //initially no nodes have been inserted for (int i = 0; i < locations.length; i++) locations[i] = -1; size = 0;

13 Binary Heap public void removemin() { //PRE: getsize()!= 0 //removes the highest priority item in the queue public int getminnode() { //PRE: getsize()!= 0 //returns the highest priority node public int getmindistance() { //PRE: getsize()!= 0 //returns the distance of highest priority node

14 Binary Heap public boolean full() { //return true if the heap is full otherwise return false public void insert(int n, int d) { //PRE!full() and!inserted(n)) public void decreasekey(int n, int d) { //PRE inserted(n) and d < the distance associated with n //replace the current distance associated with n with d

15 Binary Heap public int getsize() { //return the number of values (priority, tree) pairs in the heap public boolean inserted(int n) { return locations[n]!= -1;

16 Dijkstra s Shortest Path Algorithm In the following let Distance(X) be the best estimate of the distance to X, let weight(a, B) be the weight on the edge from A to B and let Previous(Y) be the node immediately before Y on the path whose distance is the best estimate of the distance to Y Set Distance(A) to 0 For all other nodes, X, set Distance(X) to infinity repeat until the distance to all nodes is known choose a node, Z, marked unknown such that Distance(Z) is less than Distance(Y) for any Y marked unknown mark Z as known for each node, W, adjacent to Z if Distance (Z) + weight(z, W) < Distance (W) then set Distance (W) to Distance (Z) + weight(z, W) set Previous(W) to Z 16

17 Homework 6 Submission Send me only 2 Java files. The files should be called Dijkstra.java and BinaryHeap.java In the subject field of the put the value CS340 H6 The first line of each file must be a comment with your name. Add comments to each private method or additional instance variables you add