edu.princeton.cs.algorithms.Digraph Maven / Gradle / Ivy
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package edu.princeton.cs.algorithms;
/*************************************************************************
* Compilation: javac Digraph.java
* Execution: java Digraph filename.txt
* Dependencies: Bag.java In.java StdOut.java
* Data files: http://algs4.cs.princeton.edu/42directed/tinyDG.txt
*
* A graph, implemented using an array of lists.
* Parallel edges and self-loops are permitted.
*
* % java Digraph tinyDG.txt
* 13 vertices, 22 edges
* 0: 5 1
* 1:
* 2: 0 3
* 3: 5 2
* 4: 3 2
* 5: 4
* 6: 9 4 8 0
* 7: 6 9
* 8: 6
* 9: 11 10
* 10: 12
* 11: 4 12
* 12: 9
*
*************************************************************************/
import java.util.InputMismatchException;
import java.util.NoSuchElementException;
import edu.princeton.cs.introcs.In;
import edu.princeton.cs.introcs.StdOut;
/**
* The Digraph class represents a directed graph of vertices
* named 0 through V - 1.
* It supports the following two primary operations: add an edge to the digraph,
* iterate over all of the vertices adjacent from a given vertex.
* Parallel edges and self-loops are permitted.
*
* This implementation uses an adjacency-lists representation, which
* is a vertex-indexed array of {@link Bag} objects.
* All operations take constant time (in the worst case) except
* iterating over the vertices adjacent from a given vertex, which takes
* time proportional to the number of such vertices.
*
* For additional documentation,
* see Section 4.2 of
* Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class Digraph {
private final int V;
private int E;
private Bag[] adj;
/**
* Initializes an empty digraph with V vertices.
* @param V the number of vertices
* @throws java.lang.IllegalArgumentException if V < 0
*/
public Digraph(int V) {
if (V < 0) throw new IllegalArgumentException("Number of vertices in a Digraph must be nonnegative");
this.V = V;
this.E = 0;
adj = (Bag[]) new Bag[V];
for (int v = 0; v < V; v++) {
adj[v] = new Bag();
}
}
/**
* Initializes a digraph from an 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.
* @param in the input stream
* @throws java.lang.IndexOutOfBoundsException if the endpoints of any edge are not in prescribed range
* @throws java.lang.IllegalArgumentException if the number of vertices or edges is negative
*/
public Digraph(In in) {
try {
this.V = in.readInt();
if (V < 0) throw new IllegalArgumentException("Number of vertices in a Digraph must be nonnegative");
adj = (Bag[]) new Bag[V];
for (int v = 0; v < V; v++) {
adj[v] = new Bag();
}
int E = in.readInt();
if (E < 0) throw new IllegalArgumentException("Number of edges in a Digraph must be nonnegative");
for (int i = 0; i < E; i++) {
int v = in.readInt();
int w = in.readInt();
addEdge(v, w);
}
}
catch (NoSuchElementException e) {
throw new InputMismatchException("Invalid input format in Digraph constructor");
}
}
/**
* Initializes a new digraph that is a deep copy of G.
* @param G the digraph to copy
*/
public Digraph(Digraph 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 reverse = new Stack();
for (int w : G.adj[v]) {
reverse.push(w);
}
for (int w : reverse) {
adj[v].add(w);
}
}
}
/**
* Returns the number of vertices in the digraph.
* @return the number of vertices in the digraph
*/
public int V() {
return V;
}
/**
* Returns the number of edges in the digraph.
* @return the number of edges in the digraph
*/
public int E() {
return E;
}
/**
* Adds the directed edge v->w to the digraph.
* @param v the tail vertex
* @param w the head vertex
* @throws java.lang.IndexOutOfBoundsException unless both 0 <= v < V and 0 <= w < V
*/
public void addEdge(int v, int w) {
if (v < 0 || v >= V) throw new IndexOutOfBoundsException("vertex " + v + " is not between 0 and " + (V-1));
if (w < 0 || w >= V) throw new IndexOutOfBoundsException("vertex " + w + " is not between 0 and " + (V-1));
adj[v].add(w);
E++;
}
/**
* Returns the vertices adjacent from vertex v in the digraph.
* @return the vertices adjacent from vertex v in the digraph, as an Iterable
* @param v the vertex
* @throws java.lang.IndexOutOfBoundsException unless 0 <= v < V
*/
public Iterable adj(int v) {
if (v < 0 || v >= V) throw new IndexOutOfBoundsException();
return adj[v];
}
/**
* Returns the reverse of the digraph.
* @return the reverse of the digraph
*/
public Digraph reverse() {
Digraph R = new Digraph(V);
for (int v = 0; v < V; v++) {
for (int w : adj(v)) {
R.addEdge(w, v);
}
}
return R;
}
/**
* Returns a string representation of the graph.
* This method takes time proportional to E + V.
* @return the number of vertices V, followed by the number of edges E,
* followed by the V adjacency lists
*/
@Override
public String toString() {
StringBuilder s = new StringBuilder();
String NEWLINE = System.getProperty("line.separator");
s.append(V + " vertices, " + E + " edges " + NEWLINE);
for (int v = 0; v < V; v++) {
s.append(String.format("%d: ", v));
for (int w : adj[v]) {
s.append(String.format("%d ", w));
}
s.append(NEWLINE);
}
return s.toString();
}
/**
* Unit tests the Digraph data type.
*/
public static void main(String[] args) {
In in = new In(args[0]);
Digraph G = new Digraph(in);
StdOut.println(G);
}
}