edu.princeton.cs.algs4.EdgeWeightedGraph Maven / Gradle / Ivy
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/******************************************************************************
* Compilation: javac EdgeWeightedGraph.java
* Execution: java EdgeWeightedGraph filename.txt
* Dependencies: Bag.java Edge.java In.java StdOut.java
* Data files: https://algs4.cs.princeton.edu/43mst/tinyEWG.txt
* https://algs4.cs.princeton.edu/43mst/mediumEWG.txt
* https://algs4.cs.princeton.edu/43mst/largeEWG.txt
*
* An edge-weighted undirected graph, implemented using adjacency lists.
* Parallel edges and self-loops are permitted.
*
* % java EdgeWeightedGraph tinyEWG.txt
* 8 16
* 0: 6-0 0.58000 0-2 0.26000 0-4 0.38000 0-7 0.16000
* 1: 1-3 0.29000 1-2 0.36000 1-7 0.19000 1-5 0.32000
* 2: 6-2 0.40000 2-7 0.34000 1-2 0.36000 0-2 0.26000 2-3 0.17000
* 3: 3-6 0.52000 1-3 0.29000 2-3 0.17000
* 4: 6-4 0.93000 0-4 0.38000 4-7 0.37000 4-5 0.35000
* 5: 1-5 0.32000 5-7 0.28000 4-5 0.35000
* 6: 6-4 0.93000 6-0 0.58000 3-6 0.52000 6-2 0.40000
* 7: 2-7 0.34000 1-7 0.19000 0-7 0.16000 5-7 0.28000 4-7 0.37000
*
******************************************************************************/
package edu.princeton.cs.algs4;
/**
* The {@code EdgeWeightedGraph} class represents an edge-weighted
* graph of vertices named 0 through V – 1, where each
* undirected edge is of type {@link Edge} and has a real-valued weight.
* It supports the following two primary operations: add an edge to the graph,
* iterate over all of the edges incident 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 permitted.
* 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 {@link Bag} objects.
* All operations take constant time (in the worst case) except
* iterating over the edges incident to a given vertex, which takes
* time proportional to the number of such edges.
*
* For additional documentation,
* see Section 4.3 of
* Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class EdgeWeightedGraph {
private static final String NEWLINE = System.getProperty("line.separator");
private final int V;
private int E;
private Bag[] adj;
/**
* Initializes an empty edge-weighted graph with {@code V} vertices and 0 edges.
*
* @param V the number of vertices
* @throws IllegalArgumentException if {@code V < 0}
*/
public EdgeWeightedGraph(int V) {
if (V < 0) throw new IllegalArgumentException("Number of vertices 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 random edge-weighted graph with {@code V} vertices and E edges.
*
* @param V the number of vertices
* @param E the number of edges
* @throws IllegalArgumentException if {@code V < 0}
* @throws IllegalArgumentException if {@code E < 0}
*/
public EdgeWeightedGraph(int V, int E) {
this(V);
if (E < 0) throw new IllegalArgumentException("Number of edges must be nonnegative");
for (int i = 0; i < E; i++) {
int v = StdRandom.uniform(V);
int w = StdRandom.uniform(V);
double weight = Math.round(100 * StdRandom.uniform()) / 100.0;
Edge e = new Edge(v, w, weight);
addEdge(e);
}
}
/**
* Initializes an edge-weighted graph 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 and edge weights,
* with each entry separated by whitespace.
*
* @param in the input stream
* @throws IllegalArgumentException if the endpoints of any edge are not in prescribed range
* @throws IllegalArgumentException if the number of vertices or edges is negative
*/
public EdgeWeightedGraph(In in) {
this(in.readInt());
int E = in.readInt();
if (E < 0) throw new IllegalArgumentException("Number of edges must be nonnegative");
for (int i = 0; i < E; i++) {
int v = in.readInt();
int w = in.readInt();
validateVertex(v);
validateVertex(w);
double weight = in.readDouble();
Edge e = new Edge(v, w, weight);
addEdge(e);
}
}
/**
* Initializes a new edge-weighted graph that is a deep copy of {@code G}.
*
* @param G the edge-weighted graph to copy
*/
public EdgeWeightedGraph(EdgeWeightedGraph 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 (Edge e : G.adj[v]) {
reverse.push(e);
}
for (Edge e : reverse) {
adj[v].add(e);
}
}
}
/**
* Returns the number of vertices in this edge-weighted graph.
*
* @return the number of vertices in this edge-weighted graph
*/
public int V() {
return V;
}
/**
* Returns the number of edges in this edge-weighted graph.
*
* @return the number of edges in this edge-weighted graph
*/
public int E() {
return E;
}
// throw an IllegalArgumentException unless {@code 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 {@code e} to this edge-weighted graph.
*
* @param e the edge
* @throws IllegalArgumentException unless both endpoints are between {@code 0} and {@code V-1}
*/
public void addEdge(Edge e) {
int v = e.either();
int w = e.other(v);
validateVertex(v);
validateVertex(w);
adj[v].add(e);
adj[w].add(e);
E++;
}
/**
* Returns the edges incident on vertex {@code v}.
*
* @param v the vertex
* @return the edges incident on vertex {@code v} as an Iterable
* @throws IllegalArgumentException unless {@code 0 <= v < V}
*/
public Iterable adj(int v) {
validateVertex(v);
return adj[v];
}
/**
* Returns the degree of vertex {@code v}.
*
* @param v the vertex
* @return the degree of vertex {@code v}
* @throws IllegalArgumentException unless {@code 0 <= v < V}
*/
public int degree(int v) {
validateVertex(v);
return adj[v].size();
}
/**
* Returns all edges in this edge-weighted graph.
* To iterate over the edges in this edge-weighted graph, use foreach notation:
* {@code for (Edge e : G.edges())}.
*
* @return all edges in this edge-weighted graph, as an iterable
*/
public Iterable edges() {
Bag list = new Bag();
for (int v = 0; v < V; v++) {
int selfLoops = 0;
for (Edge e : adj(v)) {
if (e.other(v) > v) {
list.add(e);
}
// add only one copy of each self loop (self loops will be consecutive)
else if (e.other(v) == v) {
if (selfLoops % 2 == 0) list.add(e);
selfLoops++;
}
}
}
return list;
}
/**
* Returns a string representation of the edge-weighted 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 of edges
*/
public String toString() {
StringBuilder s = new StringBuilder();
s.append(V + " " + E + NEWLINE);
for (int v = 0; v < V; v++) {
s.append(v + ": ");
for (Edge e : adj[v]) {
s.append(e + " ");
}
s.append(NEWLINE);
}
return s.toString();
}
/**
* Unit tests the {@code EdgeWeightedGraph} data type.
*
* @param args the command-line arguments
*/
public static void main(String[] args) {
In in = new In(args[0]);
EdgeWeightedGraph G = new EdgeWeightedGraph(in);
StdOut.println(G);
}
}
/******************************************************************************
* Copyright 2002-2018, Robert Sedgewick and Kevin Wayne.
*
* This file is part of algs4.jar, which accompanies the textbook
*
* Algorithms, 4th edition by Robert Sedgewick and Kevin Wayne,
* Addison-Wesley Professional, 2011, ISBN 0-321-57351-X.
* http://algs4.cs.princeton.edu
*
*
* algs4.jar is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* algs4.jar is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with algs4.jar. If not, see http://www.gnu.org/licenses.
******************************************************************************/