130 lines
4.0 KiB
Java
130 lines
4.0 KiB
Java
import java.util.ArrayList;
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import java.lang.StringBuilder;
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class AdjacencyListGraph<E extends Comparable<E>> {
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ArrayList<Vertex> verticies;
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public AdjacencyListGraph() {
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verticies = new ArrayList<>();
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}
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private class Vertex {
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E data;
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ArrayList<Vertex> adjacentVerticies;
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public Vertex(E data) {
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adjacentVerticies = new ArrayList<>();
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this.data = data;
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}
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public boolean addAdjacentVertex(Vertex to) {
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for (Vertex v: adjacentVerticies) {
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if (v.data.compareTo(to.data) == 0) {
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return false; // the edge already exists
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}
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}
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return adjacentVerticies.add(to); // this will return true;
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}
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public boolean removeAdjacentVertex(E to) {
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// use indexes here so it is possible to
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// remove easily without implementing
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// equals method that ArrayList.remove(Object o) uses
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for (int i = 0; i < adjacentVerticies.size(); i++) {
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if (adjacentVerticies.get(i).data.compareTo(to) == 0) {
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adjacentVerticies.remove(i);
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return true;
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}
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}
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return false;
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}
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}
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/**
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* this method removes an edge from the graph between two specified
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* verticies
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*
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* @param from the data of the vertex the edge is from
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* @param to the data of the vertex the edge is going to
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* @return returns false if the edge doesn't exist, returns true if the edge exists and is removed
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*/
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public boolean removeEdge(E from, E to) {
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Vertex fromV = null;
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for (Vertex v: verticies) {
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if (from.compareTo(v.data) == 0) {
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fromV = v;
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break;
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}
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}
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if (fromV == null) return false;
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return fromV.removeAdjacentVertex(to);
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}
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/**
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* this method adds an edge to the graph between two specified
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* verticies
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*
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* @param from the data of the vertex the edge is from
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* @param to the data of the vertex the edge is going to
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* @return returns true if the edge did not exist, return false if it already did
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*/
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public boolean addEdge(E from, E to) {
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Vertex fromV = null, toV = null;
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for (Vertex v: verticies) {
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if (from.compareTo(v.data) == 0) { // see if from vertex already exists
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fromV = v;
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} else if (to.compareTo(v.data) == 0) { // see if to vertex already exists
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toV = v;
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}
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if (fromV != null && toV != null) break; // both nodes exist so stop searching
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}
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if (fromV == null) {
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fromV = new Vertex(from);
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verticies.add(fromV);
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}
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if (toV == null) {
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toV = new Vertex(to);
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verticies.add(toV);
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}
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return fromV.addAdjacentVertex(toV);
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}
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/**
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* this gives a list of verticies in the graph and their adjacencies
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*
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* @return returns a string describing this graph
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*/
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public String toString() {
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StringBuilder sb = new StringBuilder();
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for (Vertex v: verticies) {
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sb.append("Vertex: ");
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sb.append(v.data);
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sb.append("\n");
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sb.append("Adjacent verticies: ");
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for (Vertex v2: v.adjacentVerticies) {
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sb.append(v2.data);
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sb.append(" ");
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}
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sb.append("\n");
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}
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return sb.toString();
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}
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}
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public class Graphs {
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public static void main(String args[]) {
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AdjacencyListGraph<Integer> graph = new AdjacencyListGraph<>();
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assert graph.addEdge(1, 2);
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assert graph.addEdge(1, 5);
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assert graph.addEdge(2, 5);
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assert !graph.addEdge(1, 2);
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assert graph.addEdge(2, 3);
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assert graph.addEdge(3, 4);
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assert graph.addEdge(4, 1);
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assert !graph.addEdge(2, 3);
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System.out.println(graph);
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}
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}
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