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undirectedGraph.java
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140 lines (127 loc) · 3.99 KB
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/**
* A graph implemented with array of sets.
* Parallel edges and self-loops are allowed.
*
*/
import java.util.NoSuchElementException;
/**
* The `Graph` class represents an undirected graph of vertices named 0 through `V` - 1.
* It supports the following two primary operations: add an edge to the graph,
* iterate over all of the vertices adjacent to a vertex. It also provides methods
* for returning the number of vertices `V` and the number of edges `E`. Parallel
* edges and self-loops are allowed.
* By convention, a self-loop `v-v` appears in the adjacency list of `v` twice and contributes
* two to the degree of `v`.
*
* This implementation uses an adjacency-lists representation, which is a vertex-indexed
* array of `Bag` objects.
* All operations take constant time(in the worst case) except iterating over the
* vertices adjacent to a given vertex, which takes time proportional to the number
* of such vertices.
*
*/
public class Graph {
private static final String NEWLINE = System.getProperty("line.separator");
private final int V;
private int E;
private Bag<Integer>[] adj;
/* Initializes an empty graph with `V` vertices and 0 edges. */
public Graph(int V) {
if(V < 0)
throw new IllegalArgumentException("Number of vertices must be non-negative");
this.V = V;
this.E = 0;
adj = (Bag<Integer>[]) new Bag[V];
for(int v = 0; v < V; v++)
adj[v] = new Bag<Integer>();
}
/* Initializes a graph from the specified input stream.
* The format is the number of vertices `V`, followed by the number of edges `E`,
* followed by `E` pairs of vertices, with each entry separated by whitespace.
*
*/
public Graph(In in) {
try{
this.V = in.readInt();
if(V < 0)
throw new IllegalArgumentException("number of vertices in a Graph must be non-negative");
adj = (Bag<Integer>[]) new Bag[V];
for(int v = 0; v < V; v++)
adj[v] = new Bag<Integer>();
int E = in.readInt();
if(E < 0)
throw new IllegalArgumentException("number of edges in a Graph must be non-negative");
for(int i = 0; i < E; i++) {
int v = in.readInt();
int w = in.readInt();
validateVertex(v);
validateVertex(w);
addEdge(v, w);
}
} catch(NoSuchElementException e) {
throw new IllegalArgumentException("invalid input format in Graph constructor", e);
}
}
/* initializes a new Graph that is a deep copy of `G` */
public Graph(Graph G) {
this(G.V());
this.E = G.E();
for(int v = 0; v < G.V(); v++) {
// reverse so that adjacency list is in same order as original
Stack<Integer> reverse = new Stack<Integer>();
for(int w:G.adj[v])
reverse.push(w);
for(int w:reverse)
adj[v].add(w);
}
}
/* return the number of vertices in this graph. */
public int V() {
return v;
}
/* returns the number of edges in this graph. */
public int E() {
return E;
}
// throws an IllegalArgumentException unless (0 <= v < V)
private void validateVertex(int v) {
if(v < 0 || v >= V)
throw new IllegalArgumentException("vertex " + v + " is not between 0 and " + (V - 1));
}
/* adds the undirected edge v-w to this graph. */
public void addEdge(int v, int w) {
validateVertex(v);
validateVertex(w);
E++;
adj[v].add(w);
adj[w].add(v);
}
/* returns the vertices adjacent to vertext `v` */
public Iterable<Integer> adj(int v) {
validateVertex(v);
return adj[v];
}
/* returns the degree of vertext `v` */
public int degree(int v) {
validateVertex(v);
return adj[v].size();
}
/* returns a string representation of this graph */
public String toString() {
StringBuilder s = new StringBuffer();
s.append(V + " vertices, " + E + " edges " + NEWLINE);
for(int v = 0; v < V; v++) {
s.append(v + ": ");
for(int w:adj[v])
s.append(w + " ");
s.append(NEWLINE);
}
return s.toString();
}
/* test */
public static void main(String[] args) {
In in = new In(args[0]);
Graph G = new Graph(in);
StdOut.println(G);
}
}